Optical fan-out and broadcast interconnect

ABSTRACT

Methods and apparatus are described for an optical fan-out and broadcast interconnect. A method includes operating an optical fan-out and broadcast interconnect including: fanning-out an optical signal from an optical signal emitter, of one of a plurality of nodes, with a diverging element of one of a plurality of optics; and broadcasting the optical signal to one of a plurality of receivers of all of the plurality of nodes with a light collecting and focusing element of all of the plurality of optics, wherein the plurality of optics are positioned to define an optics array, the plurality of receivers are positioned to define a receiver array that corresponds to the optics array and the plurality of nodes are positioned to define a node array that substantially corresponds to the receiver array and the optics array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims a benefit of priority under 35 U.S.C. 119(e)from both copending provisional patent application U.S. Ser. No.60/423,939, filed Nov. 5, 2002 and copending provisional patentapplication U.S. Ser. No. 60/432,141, filed Dec. 10, 2002, the entirecontents of both of which are hereby expressly incorporated herein byreference for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of optical interconnectsfor computer systems and/or their subsystems as well as networks and/ortheir subsystems. More particularly, the invention relates to afree-space optical interconnect that includes a fan-out and broadcastsignal link.

2. Discussion of the Related Art

The concept of parallel-distributed processing (PDP), which is thetheory and practice of massively parallel processing machines, predatesthe first supercomputers of the 1960s. In practice, high-performanceparallel-distributed processing machines are difficult to achieve forseveral interrelated reasons. On the physical side of the equation,interconnections between n processors or nodes increase as the square ofthe number of processors (n²); the physical bulk increases as n for thepackaging and n² for the interconnecting wiring; latency due tocapacitance increases as the average distance between nodes, which isalso proportional to n; heat-removal difficulty increases as the squareroot of the number of processors (n^(1/2)) due to the surface-to-volumeratio. On the logical side of the equation, message overhead is constantfor broadcast mode and can increase as n for relay mode. The impact onsoftware is roughly proportional to n² due to the increased complexityof parallel-distributed processing algorithms. The overall cost per nodeincreases more rapidly than the number of nodes when all these factorsare considered. What is needed is a method of parallel-distributedprocessing, design and operation that overcomes some or all of thesescaling problems.

The present record holder in performance is NEC's “Earth Simulator”topping out at 35.86 teraflops (a teraflop is 1000 gigaflops and a flopis a floating-point operation while “flops” usually refers to a flop persecond). While there are many interesting and novel entries in today'ssupercomputer marathon, the Department of Energy's Advanced Simulationand Computing Initiative (ASCI) has sponsored several of the topcontenders. The latest of these is a fifth-generation ASCI system to bebuilt by IBM. The ASCI Purple (AP), if on time and within budget, willarrive by 2005 at a projected cost of approximately $550 per gigaflopwith an ultimate option to have a 100-teraflops performance figure in asingle machine. (A gigaflop is one billion operations per second.) Thisis about 12 times the performance of the previous ASCI Q and ASCI Whitemachines. By contrast, a present-day personal computer is typicallypriced about $750/GF (the minimum cost is probably about $500/GF, i.e.,actually less than the ASCI Purple.) This clearly shows that economiesof scale are nonexistent to marginal given the factor of nearly 13,000increase in the number of processors required to achieve the 100teraflop (TF) figure. (A teraflop is 1000 gigaflops.) The ASCI Purple(AP) is estimated to weight in at 197 tons and cover an area of twobasketball courts (volume not specified). The AP will have 12,433 Power5microprocessors, a total memory bandwidth of 156,000 GBs (gigabytes perseconds), and approximately 50 terabytes (million megabytes) of memory.Power dissipation will be between 4 and 8 MW (megawatts), countingmemory, storage, routing hardware and processors.

IBM's Blue Gene™/L (BGL), based on that company's system-on-chip (SOC)technology, will take up four times less space and consume about 5 timesless power, it is expected to perform at the 300 to 400 teraflops level.The cost per gigaflop will be about the same at about $600/GF as above.Each of the 65,000 nodes in the BGL will contain two Power PCs, fourfloating-point units, 8 Mbytes of embedded DRAM, a memory controller,support for gigabit Ethernet, and three interconnect modules. The totalnumber of transistors is expected to be around 5 million, making for alarge, expensive, and relatively power-hungry node. The interconnecttopology is that of a torus, where each node directly connects to sixneighbors. For synchronizing all nodes in the system, hardware called a“broadcast tree” is necessary. Establishing broadcast mode to begin acomputation, for example, will require several microseconds. To roundout the hardware complement of a node, nine memory chips with connectors(for a total of 256 Mbytes) are foreseen. Four nodes will be placed on a4 by 2-inch printed-circuit card.

Reliability in these existing machines is a major concern when there arefrom hundreds-of-thousands to millions of material interconnections(e.g., wires, connectors, solder joints, contact bonding). What isneeded is an approach to super computer design that increasesreliability.

Moreover, the main, unsolved problem facing today's supercomputers ishow to achieve the economies of scale found elsewhere in the industrialworld. Machines with tens of thousands of processors cost as much pergigaflop as commodity PCs having only a single processor. Part of thereason for this lack of progress in supercomputer scaling is that theinterconnect problem has not yet found a satisfactory solution. Adoptingpresent solutions leads to a reliance on slow and bulky, off-chiphardware to carry the message traffic between processors. A relatedproblem is that communication delays increase as the number of nodesincreases, meaning that the law of diminishing returns soon sets in.This issue drives the industry to faster and faster processing nodes tocompensate for the communications bottleneck. However, using faster andmore powerful nodes increases both the cost per node and the overallpower consumption. Smaller, slower, and smarter processors could beeffectively used if the communications problem were to be solved in amore reasonable fashion.

Broadcasting is an essential feature of parallel computer interconnects.It is used for synchronization, and is intrinsic to many types ofcalculations and applications, including memory system coherency controland virtual memory. Many applications running on today's supercomputerswere written decades ago for relatively small parallel computers thathad good bandwidth for broadcasting. These programs run poorly ontoday's massively parallel machines. The commonly used interconnectsbased on cross bars and fat trees as well as all existing parallelcomputers with n interconnecting nodes consume n channels of bandwidthduring broadcasting, so the per port and bisection bandwidths do notchange substantially when broadcasting.

Massively parallel high performance computers using fat tree andcrossbar interconnect suffer from a mismatch with the softwarerequirement for non-blocking broadcast of short messages. Two of themost common network functions, Allreduce and Sync simultaneouslybroadcast one-word messages. Such broadcast uses excessive bandwidth infat-tree interconnects which results in poor system performance. Anotherfunction, termed all-to-all communications wherein each computing nodein a supercomputer frequently needs to communicate to all other nodesduring the course of a computation is an essential functional capabilityof any modern interconnect scheme. Additionally, these all-to-allmessages are typically short, being a few bytes in length. Frequentlyused algorithms requiring the all-to-all function include parallelversions of matrix transpose and inversion, Fourier transforms, andsorting. The most effective way to implement the all-to-all function isto base it on a true broadcast capability. Present systems can broadcastinformation, but only by simulating the broadcast function; thus theircapability for implementing the all-to-all function is inefficient.

A poor solution to the interconnect problem leads one directly to thegeneral assumption that the most powerful processors available should becrammed into each node to achieve good supercomputer performance, thushiding the problems inherent in the interconnect by faster

-   -   processors and higher channel bandwidth. A compromise is        possible if some of these other issues are more effectively        resolved. The compromise based on a more suitable interconnect        would make use of processors not quite on the leading edge of        integration and performance    -   to create a supercomputer of lower cost and power consumption        with just as great, or more, overall capability. Of course,        nothing prevents one from using the ultra-performance processors        as nodes in the proposed systems; both cost and capability would        rise significantly.

Today's supercomputer architecture at most makes use of 8-waymultithreading, meaning that there is hardware support for up to 8independent program threads. Any multitasking to be found is handled bysoftware. While theoretically alleviating the communications bottle-neckproblem and helping to overcome data-dependency issues, the cure isliterally worse than the disease since the nodes now spend more timemanaging the system's tasks in software than is gained by decomposingcomplex programs into tasks in the first place. What is needed is ascalable and cost effective approach to supercomputers that range insize from a briefcase to a small office building, and in performancefrom a few teraflops to a few petaflops. (A petaflop is 1000 teraflops.)

Interconnect schemes today are invariably based on material busses andcross bars. As data rates increase and data processors become faster,electrical communication between data-processing nodes becomes morepower intensive and expensive. As the number of processing nodescommunicating within a system increases, electrical communication becomeslower due to increased distance and capacitance as well as morecumbersome due to the geometric increase in the number of wires, thevolume of the crossbar, as well as its mass and power consumption.Electrical interconnects are reaching their limit of applicability. Asspeed requirements increase to match the capacity of ever fasterprocessors for handling data, faster electrical interconnects should bebased on controlled-impedance transmission lines whose terminationsincrease power consumption. Even the use of microstrip lines is only apartial solution as, in any fully-connected system, such lines shouldcross (in different board layers). Close proximity of communicationchannels produces crosstalk, which is perceived as noise on adjacentchannels. Neither of these problems occur in a light-based interconnect.

Optical interconnects, long recognized to be the ideal solution, arestill in the experimental stage with practical optical systemsconnecting only a handful of processors. The main problem with today'soptical solutions is conceptual: they are trying to solve a morecomplicated problem than necessary. This restrictive view has itsorigins in a limited version of a task or thread: if CPU overhead isrequired to switch from a computational task to a communications taskevery time a message arrives, any conceivable computation spread acrossa multiprocessor system will soon be spending most all of its time onswitching overhead. The way around this untenable situation is to createliteral, point-to-point connections as is done for the Hypercube™ andManhattan architectures such as the Transputer™. Thus, the source anddestination of every message is determined by hard-wired connections.This idea is carried over into optical schemes where there is an emitterdedicated to every receiver and a single receiver for every emitter. Foran optical system serving hundreds of thousands of nodes, the mechanicalalignment is an insurmountable nightmare.

Over the years, a number of universities and private and governmentlaboratories have investigated free space optical interconnect (FSOI)methods for multiprocessor computing, communications switching, databasesearching, and other specific applications. The bulk of the research andimplementation of FSOI has been in finding ways to achievepoint-to-point communications with narrow beams of light from multiplearrays of emitters, typically narrow-beam lasers, and multiple arrays ofphotoreceivers. The development of vertical-cavity, surface-emittinglasers (VCSELs) and integrated arrays of VCSELs has been the mainimpetus behind research in narrow-beam FSOI area. The main problems withFSOI to overcome are alignment, where each laser must hit a specificreceiver, and mechanical robustness. U.S. Pat. No. 6,509,992specifically addresses the problem of misalignment and robustness bydisclosing a system of redundant optical paths. When misalignment isdetected by a channel-monitoring device, an alternate path is chosen.

Both unfolded configurations, where an array of emitters transmits lightacross a space to an array of receivers, and folded configurations,where the emitters and receivers lie in the same plane, have beenattempted. Most FSOI methods lack direct broadcast capability due to theone-emitter, one-receiver assumption.

Point-to-point optical communications, wherein a narrowly focused laserbeam communicates information to a single receiver, represents theextreme case of an optical fan-out of one. A variation is to split anarrowly focused laser beam using one or more beam splitters, each beamsplitting producing two beams from the original. In this way, a singlenarrow beam can be split into 2^(j) beams by j beam splitters, achievingan optical fan-out of a single narrow beam into multiple narrow, butweaker, beams. However, since the receivers are typically small devices,perhaps a tenth of a millimeter in diameter, it is difficult to achieveand maintain optical alignment of the narrow laser beam onto one or morereceivers across all but the smallest distances.

A similar method of fan-out has been achieved by use of a diffractiveelement such as a hologram that splits a single beam into a multiplicityof beams. U.S. Pat. No. 6,452,700 discloses an FSOI backplane based onholographic optical elements mounted on an expansion card. This approachalso suffers from sensitivity to alignment which is augmented bytemperature sensitivity of the hologram material that affects the sizeof the fan-out pattern. In a typical implementation of a four-node,point-to-point optical interconnect whose linear dimensions areapproximately 100 mm, the constraint on angular alignment of the narrowbeam is 1/20th of a degree. Severity of this constraint increaseslinearly with the size of the interconnect.

What is needed is a cost effectively scalable approach to opticalinterconnection that is not sensitive to alignment issues.

SUMMARY OF THE INVENTION

There is a need for the following aspects of the invention. Of course,the invention is not limited to these aspects.

According to an aspect of the invention, a process comprises operatingan optical fan-out and broadcast interconnect including: fanning-out anoptical signal from an optical signal emitter, of one of a plurality ofnodes, with a diverging element of one of a plurality of optics; andbroadcasting the optical signal to one of a plurality of receivers ofall of the plurality of nodes with a light collecting and focusingelement of all of the plurality of optics, wherein the plurality ofoptics are positioned to define an optics array, the plurality ofreceivers are positioned to define a receiver array that corresponds tothe optics array and the plurality of nodes are positioned to define anode array that substantially corresponds to the receiver array and theoptics array. According to another aspect of the invention, amanufacture comprises an optical fan-out and broadcast interconnectincluding: a plurality of nodes positioned to define a node array, eachof the plurality of nodes having an optical signal emitter and aplurality of optical signal receivers positioned to define a receiverarray that substantially corresponds to the node array; and a pluralityof optics optically coupled to the array of nodes, the plurality ofoptics positioned to define an optics array that substantiallycorresponds to the node array and the receiver array, each of theplurality of optics including a diverging element and a light collectingand focusing element, wherein an optical signal from the optical signalemitter is fanned-out by the diverging element of one of the optics andbroadcast to one of the plurality of receivers of all of the pluralityof nodes by the light collecting and focusing element of all of theplurality of optics. According to another aspect of the invention, aprocess comprises operating a lightnode including: fanning-out anoptical signal through a diverging element; broadcasting the opticalsignal through a light collecting and focusing element; and receivingthe optical signal with one of a plurality of receivers, wherein theplurality of receivers are positioned to define a receiver array.According to another aspect of the invention, a manufacture comprises alightnode including: a diverging element; a light collecting andfocusing element optically coupled to the diverging element; and areceiver array optically coupled to the light collecting and focusingelement, the receiver array having a plurality of optical signalreceivers positioned to define the receiver array. According to anotheraspect of the invention, a manufacture comprises a node array includinga plurality of nodes positioned to define the node array, each of theplurality of nodes having an optical signal emitter and a plurality ofoptical signal receivers positioned to define a receiver array thatsubstantially corresponds to the node array. According to another aspectof the invention, a manufacture comprises an optic array including aplurality of optics positioned to define the optics array, each of theplurality of optics including a diverging element and a light collectingand focusing element.

These, and other, aspects of the invention will be better appreciatedand understood when considered in conjunction with the followingdescription and the accompanying drawings. It should be understood,however, that the following description, while indicating variousembodiments of the invention and numerous specific details thereof, isgiven by way of illustration and not of limitation. Many substitutions,modifications, additions and/or rearrangements may be made within thescope of the invention without departing from the spirit thereof, andthe invention includes all such substitutions, modifications, additionsand/or rearrangements.

The drawings accompanying and forming part of this specification areincluded to depict certain aspects of the invention. A clearerconception of the invention, and of the components and operation ofsystems provided with the invention, will become more readily apparentby referring to the exemplary, and therefore nonlimiting, embodimentsillustrated in the drawings, wherein identical reference numeralsdesignate the same elements. The invention may be better understood byreference to one or more of these drawings in combination with thedescription presented herein. It should be noted that the featuresillustrated in the drawings are not necessarily drawn to scale.

FIG. 1 illustrates a schematic perspective view of a subassemblyincluding a mirror and lens array, representing an embodiment of theinvention.

FIGS. 2A and 2B illustrate schematic perspective views of light raysfrom an emitter on a wafer opposite a mirror without (FIG. 2A) and with(FIG. 2B) a diverging lens, representing an embodiment of the invention.

FIG. 3 illustrates a schematic cross sectional view of light rays froman emitter through an unfolded wafer-mirror-lens array assembly,representing an embodiment of the invention.

FIG. 4 illustrates a schematic normal view of a composite lens assemblyincluding a converging lens array and a diverging lens array,representing an embodiment of the invention.

FIG. 5 illustrates a schematic perspective view of the composite lensassembly shown in FIG. 4, representing an embodiment of the invention.

FIG. 6 illustrates a schematic normal view of an alternative compositeoptic including a converging lens and a diverging element in coaxialalignment with the converging lens, representing an embodiment of theinvention.

FIG. 7A illustrates a schematic perspective views of an enclosed opticalinterconnect assembly including a heat exchanger, a power grid, acircuit wafer, a lens array and a mirror, representing an embodiment ofthe invention.

FIGS. 7B-7C illustrate schematic side (FIG. 7B) and normal (FIG. 7C)views of the enclosed optical interconnect assembly shown in FIG. 7A,representing an embodiment of the invention.

FIG. 8 illustrate a schematic normal view of a circuit wafer including aplurality of computer nodes each of which includes four optical signalsources (emitters), representing an embodiment of the invention.

FIGS. 9A and 9B illustrate schematic normal (FIG. 9A) and side (FIG. 9B)views of an individual computer node including four optical signalsources, representing an embodiment of the invention.

FIG. 10 illustrates a schematic perspective view of a power supply busbar assembly, representing an embodiment of the invention.

FIG. 11 illustrates a schematic perspective view of two substantiallyorthogonal components of a light baffle assembly, representing anembodiment of the invention.

FIG. 12 illustrates a schematic perspective view of a light baffleassembly coupled to a plurality of individual computer nodes arranged ina wafer configuration, representing an embodiment of the invention.

FIG. 13 illustrates a schematic side view of a system including anoptical computer assembly with a partially transmissive mirror coupledto an interface array via an optical link, representing an embodiment ofthe invention.

FIG. 14 illustrates a schematic side view of an interface arraysubassembly, representing an embodiment of the invention.

FIGS. 15A-15C illustrate schematic side views of three optical computermeta-assemblies, representing embodiments of the invention.

FIG. 16 illustrates a schematic side view of a systolic optical computermeta-assembly including four optical computers, representing anembodiment of the invention.

FIG. 17 illustrates a schematic side view of fan-out (broadcast) from anoptical signal emitter via a diverging lens, representing an embodimentof the invention.

FIG. 18 illustrates a schematic side view of convergence from fan-outvia a plurality of converging lenses, representing an embodiment of theinvention.

FIG. 19 illustrates a schematic side view of convergence from amultiplicity of fan-outs via a plurality of converging lenses,representing an embodiment of the invention.

FIGS. 20A and 20B illustrate schematic normal views of single emittermodules having detector arrays configured for deployment of the modulesas part of a 5 by 5 interconnect array, representing an embodiment ofthe invention.

FIGS. 21A-21C illustrates schematic normal views of a one emitter module(FIG. 21A), a four emitter module (FIG. 21B) and an eight emitter module(FIG. 21C), representing an embodiment of the invention.

FIG. 22 illustrates a schematic side view of a single converging lens,representing an embodiment of the invention.

FIGS. 23A and 23B illustrate schematic normal (FIG. 23A) and crosssectional (FIG. 23B) views of a composite diverging-converging opticconfigured for deployment in conjunction with modules having fouremitters, representing an embodiment of the invention.

FIG. 24 illustrates a schematic perspective view of a collecting andfocusing lens optically coupled to a detector, showing a focal point anda plane defined by the detector, representing an embodiment of theinvention.

FIGS. 25A and 25B illustrate schematic bottom normal (FIG. 25A) and topnormal (FIG. 25B) views of a node including four processing nodes(modules), four emitters and 36 detectors implying deployment of thenode in a 3 by 3 node array, representing an embodiment of theinvention.

FIG. 26 illustrates a schematic normal view of a 3 by 3 module arrayshowing asymmetric alignment of the optics corresponding to the fourmodules at the upper right of the module array, representing anembodiment of the invention.

FIG. 27 illustrates a schematic perspective view of a node includingfour processing nodes (modules) each of which includes four subsections,representing an embodiment of the invention.

FIGS. 28A and 28B illustrate schematic bottom normal (FIG. 28A) and topnormal (FIG. 28B) views of a node with four processing nodes (modules),representing an embodiment of the invention.

FIG. 29 illustrates a schematic perspective view of an opticalinterconnect including a 3 by 3 node array, a 3 by 3 optic array and amirror, representing an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention and the various features and advantageous details thereofare explained more fully with reference to the nonlimiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well known starting materials,processing techniques, components and equipment are omitted so as not tounnecessarily obscure the invention in detail. It should be understood,however, that the detailed description and the specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only and not by way of limitation. Various substitutions,modifications, additions and/or rearrangements within the spirit and/orscope of the underlying inventive concept will become apparent to thoseskilled in the art from this disclosure.

The below-referenced U.S. Patents disclose embodiments that are usefulfor the purposes for which they are intended. The entire contents ofU.S. Pat. Nos. 6,538,818; 6,509,992; 6,452,700; 6,445,326; 6,208,672;6,163,642; 6,016,211; 5,987,601; 5,965,873; 5,864,642; 5,778,015;5,703,707; 5,541,914; 5,465,379; 5,548,772; 5,546,209; 5,446,572;5,432,722; 5,420,954; 5,414,819; 5,412,506; 5,297,068; 5,228,105;5,159,473; 5,146,358; 4,953,954; 4,943,136; and 4,870,637 are all herebyexpressly incorporated by reference herein for all purposes. Thebelow-referenced U.S. Patent Applications disclose embodiments that areuseful for the purposes for which they are intended. The entire contentsof U.S. Ser. No. 10/175,621, filed Jun. 20, 2002 and PCT/US03/19175,filed Jun. 18, 2003 both by Brian T. Donovan & William B. Dress andentitled “Pulse Width and/or Position Modulation and/or Demodulation”are hereby expressly incorporated by reference for all purposes. Theentire contents of U.S. Ser. No. 60/290,919, filed May 14, 2001 andPCT/US02/15191, filed May 13, 2002 (published Nov. 21, 2002 as WO02/093752) all by Brian T. Donovan et al. are all hereby expresslyincorporated by reference for all purposes. The entire contents of U.S.Ser. No. 10/227,050, Aug. 23, 2002 “Dynamic Multilevel Task ManagementMethod and Apparatus” by Brian T. Donovan, Ray S. McKaig, and William B.Dress are hereby expressly incorporated by reference for all purposes.

Optical Backplane Disclosure

A massively parallel processing (MPP) system can include an array ofprocessor modules or computing nodes that are interconnected. Inpractice, each processor node is an independent die or “chip” that couldbe individually packaged and would thereby serve as a fully functionalmicroprocessor with its standard power, ground, data buses, memoryports, and so on. Much of the expense in a modern processing system liesin the packaging of an individual die and the extension supportnecessary to provide power to and communicate with each processor in thesystem. If the individual processor dies could be connected by nearestneighbor communications buses for example, and the entire array ofprocessors be retained as a single functioning module without destroyingthe wafer, it might be possible to power each processor node andcommunicate with the entire array. In this view, the wafer of processorsbecomes the computing element at a much lower cost and higher throughputthan would be incurred by separately packaging, remounting, powering,and communicating with each individual processor.

For the wafer of processors or a collection of multi-chip modules or acollection of printed-circuit board modules to be an effective andfunctional system, n integration or close geometric coupling of theindividual processor node should be implemented. Past efforts havecentered around wafer-scale bus architectures for linking all processorstogether. The disadvantages of this approach are slow communicationspeed between processors due to the long bus structures and theattendant high capacitance. Other approaches have been attempted tocommunicate between nodes using various optical methods. A recentfavorite is to have n laser emitters and n laser receivers on each nodewhere n is the number of nodes on the wafer. This point-to-pointcommunication allows each node to individually talk directly to anyother but involves a total surface area of 2n²×A, where A is the area ofan emitter or receiver, typically a region of about 100 μm on a side. Byswitching to a broadcast model where each node has a single emitter butn receivers, this overhead is cut in half. More importantly, thecommunications traffic handled by each node in the case of “fullyconnected” wafer can easily overload the computational capacity of thenode itself for both transmission and reception. In the broadcast model,where each node has but a single emitter, the transmission load isapproximately n times less while the receiving communications load canbe maximal if needed. Clearly a communications protocol should beestablished to decide whether a particular transmitted message is for aparticular node as any given emitter talks to all nodes. If the nodesare indexed or numbered for identification purposes, a map may beconstructed for each node in the array. This map specifies whichreceiver on a given node is optically linked to which particularemitter. Each receiver is then monitored by a task or a circuit runningon the node in question, said task or circuit identifying receivedmessages for the receiving node and ignoring others.

A goal of an optical backplane is to provide a parallel interconnectionstructure, connecting each node to every other node on the wafer. Oneapproach to providing such an optical interconnect is to employ an arrayof lenses and a mirror as illustrated in FIG. 1.

Referring to FIG. 1, a mirror 110 is shown on the left of the figurewith a 3×3 lens array 120 to the right of the mirror, and centered onthe mirror axis. An array of computing nodes (not shown) would lie tothe right of the lens array. The mirror 110, the array 120 and the arrayof computing nodes can all be contained within an enclosure 130,optionally under partial vacuum.

A design that optimally matches the array of nodes is to place an arrayof converging lenses where each lens has the same dimensions as theunderlying node and the array thus formed is placed directly over thearray of nodes. As shown in FIGS. 4-6, the lens array preferablyincludes both diverging elements and converging elements. The functionof the diverging elements, whether light pipes, thick optical fibers,negative conical lenses or the usual diverging (concave) sphericallenses, is to spread the light from each emitter to cover at least halfof the mirror area so that upon reflection, the emitter in questionilluminates at least the entire lens array so that every node on thewafer receives light from each emitter. This desired property isillustrated in FIGS. 2A and 2B.

Referring to FIGS. 2A-2B, a wafer 210 is depicted as the bottom diskwith an emitter 220 shown as the centered dot and a mirror 230 isrepresented by the top disk. If the emittance cone of the emitter 220 is8°, which is typical for a VCSEL laser, a set of typical rays is shownwith direct rays diverging from bottom to top and reflected raysdiverging from top to bottom. FIG. 2B is similar to FIG. 2A, butincludes a diverging lens 240 above the centered emitter 220. In FIG.2B, the entire wafer array is covered by the reflected light. Thediverging lens 220 is shown at the center of FIG. 2B as a small disk.

The invention can include inserting (including) a converging lens tocollect the reflected rays and focus the light onto the intendedreceivers. This situation is shown in FIG. 3.

Referring to FIG. 3, a cross section through the unfolded system isdepicted showing only half of the system (the light rays and lensesbelow zero are inferred by symmetry about the horizontal axis). An arrayof nodes 310 is on the left, with node centers at every 10 mm (centersare coordinates 0, 10, 20, . . . ). A mirror 320 is shown as thevertical line in the center at distance 50 from the wafer, only a singleemitter 330 at coordinate (0,0) is shown for clarity. Its accompanyingdiverging lens 340 is shown at about distance 10 from the wafer. Thelens array 350 is located at about position 90 is has its opticalcenters characterized by the spatial index reflection of the array 310on the left, the later of which is not shown in its entirety forclarity. The rays emitted from the light source at the wafer surfacediverge slightly and fill the diverging lens 340 where they spread outto cover about half the mirror 320 and then are reflected back onto thelens array 350. The diverging lens 340 further broadens the light whilethe converging lenses 355 of the lens array 350 focus the light on ornear the wafer whose reflection is shown at position 100. In FIG. 3,where the mirror is at a distance of 50 (half the wafer radius), thevariation in focal points across the wafer becomes obvious. There are atleast two ways to overcome this lack of focus across the entire wafer.The first is to place the mirror at a distance equal to or greater thanthe wafer radius, essentially flattening the surface defined by thefocal points, so the maximum deviation would be cut in half or more thanthe situation shown above. The second is to insert an array of n microlenses (not shown) just above each node, providing an additionalconvergence of the light onto the array of receivers. A microlens can beplaced just above each receiver at a distance consistent with goodfocusing of the converging beams onto the receiving photo transistors.

Referring to FIG. 4, a 3×3 array 400 of cross-shaped converging lenses410 is illustrated with a 3×3 array of smaller, square diverging lenses420 nominally residing at the lower left corner of the larger converginglenses 410. The diverging lenses 420 are represented as squares withmedian horizontal and vertical coordinate axes (defining divergingquadrants 430) drawn through their centers. The depicted array 400 couldbe optically coupled to a wafer with 9 or 3×3 nodes. For a wafer with256 or 16×16 nodes, a similar lens array could include 16×16cross-shaped lenses and 16×16 smaller, square diverging lenses fitted asshown for a total of 512 lenses. If the nodes are 10×10 mm in size, thecross-shaped converging lenses would also have outer dimensions of 10×10mm and the lens centers would be positioned precisely above the nodecenters, while the emitters are positioned at the lower-left corners ofthe nodes.

Referring to FIG. 5, a three-dimensional rendering of the array 400shown in FIG. 4 is illustrated. The smaller diverging lenses 420 areshown with contour plans in their centers. The array 400, and optionallythe array of nodes and the mirror can be contained within an enclosure510.

Referring to FIG. 6, an alternative embodiment is to center the emittersand place the (round or square) diverging element or possibly light pipeor optic fiber from the emitter passing through the precise center ofconverging lenses. The receiver map will of course be different in thiscase than in the case of corner (or edge) emitters. A planar view with acircular diverging lens is shown in FIG. 6. The converging portion issquare to just match the underlying node dimensions and an array formedfrom n of these compound lenses would sit just over the wafer aspictured in FIGS. 4 and 5.

Referring to FIG. 6, an alternative embodiment of an optic 610 includinga converging element 620 and a diverging element 630 is depicted. Inthis embodiment, the converging element 620 including a converging lensand the diverging element 630 includes a diverging lens. The diverginglens is located at the center of the converging lens and they arecoplanar.

Optical Backplane Supercomputer

The invention can include a unique, new computer architecture for theconstruction of backplane optical supercomputers composed of a multitudeof processors arranged in arrays reaching to full wafer scale sizeswhereby the individual processors are massively but inexpensivelyinterconnected and enabled to simultaneously communicate with each otherby virtue of the emission and reception of optical signals fromprocessor to processor through the use of a geometric matrix ofdivergent and convergent lenses so structured as to precisely positionthe signals and assure their proper spatial distribution through threedimensional space throughout the computer through the use of a mirroredbackplane reflective surface. With signals proceeding between thesystem's various processors at the speed of light, the invention permitsthe elimination of the wiring complexities that otherwise exist and arecompounded by the square of the number of supercomputer processor nodesas extra processor components are added in current supercomputer arraydesigns. The processors can be arrayed in planar fashion on siliconwafers or other fabrication material wafers in accordance with standardmanufacturing procedures. Each processor includes one or more gasplasma, laser, light-emitting diode (LED) or other type of lightemitting nodes together with light reception nodes. A lens matrix arraycontaining divergent and convergent lens facets for each separateprocessor is employed in planar fashion positioned at an appropriatedistance above the wafer with its array of processors. When light isemitted by any one or another of the processors, it passes through thedivergent aspect of its respective lens facet to a reflective mirrorappropriately positioned above the wafer and lens matrix. This lightthen strikes the mirror and is reflected back to and through theconvergent lens aspect of the receiving processor where it is internallyconverted to a signal for execution within that processor's processingmechanisms. The entire supercomputer system may be chilled and providedwith heat dissipation mechanisms as necessary. Software controls anddata inputs and outputs may be transmitted to and from the supercomputerby any one of a number of optical fiber mechanisms, or electrical orradio-frequency or other approaches

Wafer Scale Super Computer and Optical Switch

The invention can include the use of plasma gas discharge optical signalemitters, a fiber optical chip on wafer fiber interface and the use ofthree fibers for DWDM switch hierarchy. The invention can includecooling the wafer or other microprocessor substrate with a cooled liquidbath on the back of the wafer, preferably inverted. The invention caninclude a separable refrigerator and radiator. An operating temperatureof approximately 5° C. is easy and convenient to maintain. An operatingtemperature of approximately −50° C. is better because of lower noiseand higher speed. An operating temperature of approximately −100° C. iseven better but not all CMOS circuits work at this temperature withoutmodification. Condensation should be protected against. The wafer, lensarray, mirror and heat sink may be enclosed, optionally under vacuum; asimple glass cover bellows pressure equalized chamber is easy to use asthe enclosure and cost effective.

Powering the wafer or array of microprocessors can be done by dualconductor bus bars with a ceramic high capacity bypass capacitormaterial. These capacitive power supply strips are readily commerciallyavailable, and easy to manufacture. For instance, the amount of powercan be estimated at between 1 and 2 watts per node for 256 nodes on an 8inch wafer or 1024 nodes on a 12 inch wafer, for voltages between 1 and3 volts. With 16 power strips for 256 nodes, only 16-32 watts arecarried by any one power bus. These power buses can also act as lightbaffles and front glass/lens spacer supports. The perpendiculardirection can have just light baffle sections, which can be made ofglass or ceramic. The temperature coefficient of expansion for the powerstrips and/or baffles should be matched as well as possible to thewafers. The invention can include power busses having flexible tabs perwafer, glued or soldered to the nodes to allow for mismatched thermalexpansions.

Prototypical optics to implement the invention have been ray tracesimulated and are characterized by high efficiency in the 50-90% range.Each node can have a spreading lens or lenses over its emitter(s) andthen a focusing micro lens array over the sensor array. These lenses maybe molded glass or holographic or any other structure that provides thelight spreading and then collecting and focusing functions. Theinvention can include, a few inches above the lens array, a simple flatmirror that is located and optically coupled to the emitters, the lensesand the receivers (detectors). For a single wafer design, this simpleflat mirror can be a fully reflective front surface glass mirror.

The invention can include multiple wafers or substrates ofmicroprocessors linked by using a partially reflective mirror instead ofa fully reflective mirror and placing another wafer lens assemblyequidistant from the other side of the mirror. More wafers or substratescan be added, for example up to a total of approximately 4 with simpleoptics. In situations employing multiple wafers or substrates that aresimply linked together optically, an emission from any one processornode will be received the corresponding processor node on all of thewafers or substrates. In this case, the received power per sensorchannel is divided by the number of wafers or substrates plus opticallosses. If corresponding processor nodes send at the same time, themessage may be garbled. Therefore, embodiment of the invention that havethe potential for contention garbling, the software should be capable ofcollision handling as is done in most communications systems today.

Silicon is not a fast optical sensor material for the normal colors oflights used in optical communications. At infrared (IR) and visible redfrequencies, the light penetrates too deeply into the chips andgenerates carriers that take many 100's of nanosecond to diffuse to thesensing electrodes. An alternate way to get high speed out of silicon isto use blue or UV light. This light penetrates less then 1 um into thesensor. N carriers propagate at 200 ps/10 um, thus allowing thepossibility of very high speed sensing in standard CMOS with blue and UVlight. UV and blue LEDs are cost effective. Alternative embodiments ofthe invention can use lasers, LEDs or other emitters in CW (continuouswave) mode, and modulate them, but this is not preferred.

An alternative embodiment of the invention can use multiple emitters pernode, but with a single receiver per node. The multiple emitters can beof the same wavelength or of different wavelengths. The multipleemitters can be clustered together or spaced apart. In the case ofmultiple emitters of the same wavelength, broadcasts may require morepower and a given node may send different signals via different node atthe same time causing collisions. Although more power may be required,the light from all the emitters can be aggregated and thus much morelight can be received. Collisions can be avoided by logic processingwithin the node.

Another alternative embodiment of the invention can use multipleemitters and multiple receivers per processing node (module). This hasthe above advantage of allowing the optics to direct all of the energyfrom an emitter to a single receiver. It may be problematic to locate alarge number (e.g., 256) of emitters on each processor node.

A much less powerful alternative embodiment of the invention can usejust one emitter and one receiver per node. A simple fallbackimplementation design of this embodiment can use off-the-shelf laserchips in the red region or shorter wavelengths. Shorter wavelengths maybe desirable because red receivers are harder to make fast, whileretaining sensitivity. The invention can also include the use of one ormore frequency conversion crystal(s).

The interface to the outside world can be readily commercially availablecolor fiber optics which can be picked and placed directly onto thewafer using lower cost 850 nm lasers with one fiber per laser. In thiscase, a commercial multiplexer can be used to combine the data into asingle DWDM fiber or any other standard communications backbone. Theinvention can include the use of multiple frequency lasers. The standard850 nm recover devices can be mounted to the wafer. A cooled wafer is avery attractive option for low noise, long life and short fastinterconnect.

To provide the electro-optical interface, the invention can include theuse of embodiments disclosed in U.S. Ser. No. 10/175,621, filed Jun. 20,2002 and/or PCT/US03/19175, filed Jun. 18, 2003 for the transceiverswherever external standards do not forbid. Embodiments of the pulseposition and/or pulse width modulators and/or demodulators described inU.S. Ser. No. 10/175,621, filed Jun. 20, 2002 and PCT/US03/19175, filedJun. 18, 2003 are readily commercially available from Xyron Corporationand/or LightFleet Corporation, both of these companies having offices inVancouver, Wash., USA, and one or both of these companies are identifiedas the source of these embodiments by the trademark XADACOM™, but theinvention is not limited to pulse position and/or pulse width modulationand/or demodulation, much less these XADACOM™ embodiments.

The invention can be combined with standard fiber channels whichcurrently cost about $100-$200 per channel. For state of the art DWDM,160 channels are preferable.

The invention can include a parallel 2D interconnect wafer scale supercomputer without any inter-node free space interconnect optics, but withfiber optic interfaces. Nevertheless, preferred embodiments of theinvention include the inter-node optical interconnect, thereby allowingmassively more interconnect bandwidth. Even without the inter-node freespace optical interconnect, the invention can easily include thecapability of approximately 10 Gbaud per node throughput to nearestneighbors, for example, to four nearest edge neighbors only. Processingnodes (modules) that are not edge adjacent can send messages throughmultiple processing nodes (modules) in a sequential manner, albeit witha likely reduced throughput. With the free space optical interconnect,any node can receive from any other node without any blocking and thethroughput can be easily effected at 10 Gbaud per node.

The communication to the external fiber network, can use readilycommercially available diode lasers in chip form. VCSELS can be used forthe vertical signal source optics, and edge emitters can be used for thewafer edge optics. These edge emitters are very inexpensive at about5-10$ for each 850 nm, 3 mW output laser (1300 nm laser are about 20$,1550 nm: about 60$). The wavelength of 850 nm seems to be the mostpopular LAN choice for gigabit Ethernet and fiber channel. The readilycommercially available opto receivers at 850 nm, 1300 nm and 1500 nmwavelengths can be used in a 1-5 GHz range may be possible, but diemounted receivers may be preferable. The invention can include the useof plasma gas discharge emitters for these standard telecom wavelengths,further reducing the cost.

The context of the invention can include fiber optic multiplexingequipment connecting the wafer or supercomputer system to a network.Gigabit Ethernet and fiber channel standards are readily commerciallyavailable for the 850 nm 1300 and 1500 nm wavelengths.

The invention can include an optical computer that includes 1 wafer,several wafers, or just a few nodes cut from a wafer. Systolic arrays ofmany, and perhaps unlimited, wafers may be created with a differentrelaying lens array, that send to the next wafer, but receives from theprevious wafer. The last of the array can be looped back to the firstarray for continuous processing, optionally in a circular, torus orspherical configuration.

For a large switch application, 3 sets of external optical or electricalI/O would work well. Two of these three sets could combine 2 of theoutputs from a lower wider level of the hierarchy and 1 set would sendthe merged stream to the next higher level.

Referring to FIGS. 7A-7C, a circuit wafer 701 is coupled to a coolingstructure 705, such as a plate and/or backside bath. The circuit wafer701 includes gas plasma discharge optical signal emitters. The circuitwafer 701 is coupled to a power grid 702. The power grid can includelight baffles. The power grid 702 is coupled to a lens array 703. Thelens array is coupled to a mirror 704. The circuit waver 701, power grid702, lens array 703, mirror 704 are located within a gas tight enclosure706 that contains a suitable gas 707 such as N, H, He, etcetera. Part ofthe cooling structure 705 extends through the enclosure 706 to provide aheat sink that can be coupled to a heat exchanger (not shown in FIGS.7A-7C).

Referring to FIG. 8, a circuit wafer 801 includes a plurality ofindividual computer nodes 810. In this embodiment each of the individualcomputer nodes 810 includes four optical signal emitters 820 located atthe corners of each of the individual computer nodes 810.

Referring to FIGS. 9A and 9B, the invention can include an integratedcircuit embodied in a computer node 910, where the integrated circuitincludes one or more optical signal emitters. In this embodiment, thecomputer node 910 includes i) a wafer carrying a plurality ofmicroprocessors and ii) four optical signal emitters. The invention doesnot require the presence of the microprocessors and can include the useof any number of optical signal emitters. The optical signal emitterscan be plasma gas discharge emitters 920 or laser and/or photo diodes922. For instance, modulated VCSELs (vertical-cavity, surface-emittinglasers) can provide an alternative to the plasma gas discharge opticalsignal emitters.

Referring to the top of FIG. 9A, an adjacent computer node 923 isschematically depicted. Communication between nodes/wafers can beprovided by readily commercially available fiber-optics modules whichmay be integrated onto each node/wafer. The nodes can be spaced fromapproximately 25 um to approximately 5000 um (preferably fromapproximately 250 um to approximately 500 um) apart from one another.

Referring to FIG. 9B, a side view of the computer node 910 is depicted.The computer node can include an on chip lens array 921 (not depicted inFIG. 9A). An optical signal detector can be located beneath each of themembers of the chip lens array 921. Each of the optical signal emitterscan include an emitter lens and/or light pipe 924. The emitter lensand/or light pipes 924 of two or more emitters, together with thoseintegrated circuit emitters, can be combined to define an opticalbackplane, with or without the balance of the computer node 910components.

Referring to FIG. 10, a power supply strip 1050 includes a highdielectric insulator 1052 coupled between a first power supply conductor1051 and a second power supply conductor 1053. Although two conductorsand a single insulator are shown in FIG. 10, the strip can include 3, 4or more conductors. Both the first power supply conductor 1051 and thesecond power supply conductor 1053 include a plurality of flexible powertabs 1060 that can be electrically coupled o a wafer (nodes).

Referring to FIG. 11, a first light baffle slat 1103 includes aplurality of notches 1153 for assembling into a grid pattern. A secondlight baffle slat 1104 also includes a plurality of notches and is showninverted and perpendicular to the first slat prior to assembly. It canbe appreciated that the slats can be fabricated from power supply stripsif both exposed sides of each strip are covered (e.g., coated) with aninsulator layer.

Referring to FIG. 12, a plurality of power supply strips are shown beingassembled into a combined power supply bus and light baffle 1202 that iscoupled to a circuit wafer 1201. This combined structure, as well asindividual structures in alternative embodiments, can be connected tothe wafer directly, or to the wafer closely through tabs and/or spacers,or to the wafer in a spaced apart from relationship through leads and/orstand-offs.

Referring to FIG. 13, the context of the invention can include freespace optical coupling to other components, such as a 2D blade array1362 with edge mounted optical transceivers 1370. A computer or networkdevice 1360 includes a fan-out free spaced optical interconnectbackplane having a partially silvered mirror 1365. The device 1360 isoptically coupled to a wafer to blade array lens or lens array 1361through the partially silver mirror 1365. The wafer to blade array lensor lens array 1361 is optically coupled to the edge mounted opticaltransceivers 1370.

Referring to FIG. 14, an individual blade 1450 includes an opticaltransceiver 1463. The optical transceiver 1463 is coupled to a bladeprocessor 1464, a dynamic random access memory circuit 1465 and a harddrive 1466.

Referring to FIGS. 15A-15C, several different configurations ofcombinations having multiple fan-out free space optical interconnectbackplanes are depicted. The invention can include a two, or three,dimensional combination of multiple fan-out free space opticalinterconnect backplanes. Referring to FIG. 15A, a first optical supercomputer 1561 is coupled to a second optical supercomputer 1562 via apartially silvered mirror 1504. Referring to FIG. 15B, a first opticalsuper computer 1563 is coupled to a second optical supercomputer 1564without a mirror. Referring to FIG. 15C, four optical super computers1565, 1565, 1566, 1567, each having a partially silver mirror, arecoupled together via partially silvered distribution mirror 1544.

Referring to FIG. 16, a first optical super computer 1610 is opticallycoupled to a first alternative lens array 1682 for systolic operation.The first alternative lens array 1682 is optically coupled to a multiwafer mirror 1680. The multi wafer mirror 1680 is optically coupled to asecond alternative lens array 1683 that is coupled to a second opticalsuper computer 1612. The multi wafer mirror 1680 is also opticallycoupled to a third alternative lens array 1685 that is coupled to athird optical super computer 1614. The multi wafer mirror 1680 is alsooptically coupled to a fourth alternative lens array 1687 that iscoupled to a fourth optical super computer 1616. Thus, a systolic mirrorcan be defined as an add-drop relay mirror.

Cost Effective and Mobile Super Computing

The invention can simultaneously increase the upper limits of computingpower of the largest machines by a factor of 1000 and dramaticallyreduce the size and cost of existing supercomputing installations by anorder of magnitude. The invention is compatible with existingsupercomputer software and provides orders-of-magnitude greaterconnectivity than present-day supercomputers, obviating the need forhardware reconfigurability.

The invention can open new markets for a wide range of applications thatare now simply not possible for reasons of size, cost, or powerconsumption. Once these inventions are fully developed, it will bepossible to build a teraflop computer in the form factor of today'sdesktop computer. The world's first petaflop computer, fitting into asingle office room, could soon follow. The idea scales simply to theexaflop range allowing a truly massive, parallel machine, only dreamedabout today. Comparing these numbers to the world's currently mostpowerful computer, the NEC “Earth Simulator” at 36 teraflops (a mere0.036 petaflops), should engender an appreciation of the power of theinvention.

A further implication of these improvements in size, cost, and power, isto enable the portability of teraflop computing to on-site, mobile,airborne, or space applications where supercomputing today is simply notan option. Tremendous amounts of time and expense are consumed inremotely recording large amounts of data and transporting those data toa fixed supercomputer center where they are processed, analyzed, andacted upon. The time elapsed from collection to action is typicallymeasured in days to weeks. A portable supercomputer would allowsimultaneous data collection and analysis resulting in real-timedecisions on search vectors. This capability would greatly improve theproductivity of the equipment, compress the time to complete a giventask, and make possible the completion of tasks which today are simplynot contemplated.

The invention can allow a new generation of supercomputers to exceed, byseveral orders of magnitude, the performance-to-cost ratio of existingand planned systems. The invention can include zero-overhead taskswitching with hardware scheduling and synchronization of tasks coupledwith a high-performance data-flow architecture allows complex yetinexpensive computing nodes to be built. Optical integration of arraysof such nodes enables the possibility of a teraflop computer system in adesktop-sized package. The invention enables scaling a wafer-sizedsupercomputer to assemble components that range in capability fromteraflop to petaflop to exaflop machines.

As noted above, reliability in existing supercomputing machines becomesa major concern when there are hundreds-of-thousands to millions ofmaterial interconnections (wires, connectors, solder joints, contactbonding). If these mechanical, off-chip connections can be replaced withintegrated circuitry and light beams, both the rate of the data flowshould be greatly enhanced and the reliability of the entire systemgreatly increased.

The invention can include wafer-scale integration, a topic that has beenextensively studied for over 30 years. A wafer-scale computer system caninclude an array of processor modules or computing nodes that areinterconnected. In practice, each processor node is an independent dieor “chip” that could be individually packaged and would thereby serve asa fully functional microprocessor with its standard power, ground, databuses, memory ports and so on. Much of the expense in a modernprocessing system lies in the packaging of individual dies and thesupport necessary to provide power to and communicate with eachprocessor in the system. If the individual processor nodes could beconnected efficiently and the entire array of processors retained as asingle functioning module, it would then be possible to power eachprocessor node and to communicate with the entire array. In this model,an entire wafer becomes a computing element with a much lower cost andhigher throughput than would be achieved by separately packaging,remounting, powering, and communicating with discrete and individuallypackaged chips.

As also noted above, the problems with previous optical interconnectionschemes have been precision placement of light emitters and alignment ofthe optical elements. The solution proposed here avoids these problemsby using the inherent registration precision of wafer manufacturing,employing a broadcast model with at least a single emitter on each node,and by using an optic array for spreading a focusing light from theemitters.

Computational Hardware

The Gigaflop Node

Each individual node can include a single processor die containingmultiple processing units, communications hardware, and a localnetworking or communications bus. Specialized nodes can be devoted tomemory (RAM) supported by communication hardware and memory-controlhardware. By interspersing memory nodes and processor nodes on a waferor on alternate wafers, any desired ratio of compute-performance tomemory-capacity can be achieved.

To make efficient use of processor cycles in a single node wheremultiple clients should be serviced in a timely fashion, thezero-overhead-task switching described in U.S. Pat. No. 5,987,601 can beused in combination with a hardware-based, real-time-operating-system(RTOS) kernel. In this way, the invention can include a highlyefficient, transparent managing of hundreds of interacting tasks usingdynamic-priority scheduling. Thus, each receiver on each node could beviewed as an elementary task for that node so parallel messages over theentire node can be effectively managed. Embodiments of thezero-overhead-task switching described in U.S. Pat. No. 5,987,601 arereadily commercially available from Xyron Corporation and/or LightFleetCorporation, both of these companies having offices in Vancouver, Wash.,USA, and one or both of these companies are identified as the source ofthese embodiments by the trademark ZOTS™, but the invention is notlimited to zero-overhead task switching, much less these ZOTS™embodiments.

A computation can be broken into multiple tasks much as themultithreading processors treat programmed threads quasi-independently.Multithreading can hide some latency but requires state of the artcompiler or very clever programmers to achieve even modest performanceimprovement. The zero-overhead-task switching multitasking is a superset of the multithreading concept. It allows the latency hiding ofmultithreading, then adds dynamic priorities, and hardware semaphore forsynchronization; this is accomplished without thread-switching overhead.Zero-overhead-task switching hardware multitasking decouples the storageand switching elements of the task management, thus allowing very largenumbers of tasks, easily exceeding 256, to be stored compactly inon-chip RAM, without seriously impacting the single task clock speed andperformance. This is critical in a large, multiprocessor system wherehundreds of cycles may be required to access a remote piece of data.

The zero-overhead-tack switching processing engine makes effective useof data flow. However, in the case of the invention, data flow can be ona conceptually higher level than routing bits and microcode within acentral-processing unit (CPU). The invention can include a fullyasynchronous data-flow path connecting each of the functional modulescomprising the node. This data-flow interconnect (DFI) becomes much morepowerful and practical that the usual bus architectures in making use ofmessage packets. These packets are controlled on a local level,obviating the need for bus arbitration. The DFI bus is transparent tothe system programmer who only need worry about data destinations andnot how or when data arrives.

For a wafer including n nodes, each node can have at least one opticaltransmitter to broadcast information to the entire wafer and each nodecan have n photo-diode receivers to accept information from all nodes inthe wafer. Since each receiver has its own associated communicationsmodule that talks to the DFI bus, only packets destined for the node inquestion are placed on the node's DFI bus. The receiver's communicationmodule decodes the packet header, places the packet on the DFI bus withthe appropriate destination code, and waits for the next packet. Dataacknowledgment is routed on the DFI bus to the node's transmitterstation as required. This local processing allows asynchronouscommunication to take place without global control, greatly simplifyingthe communications protocol and speeding up data flow throughout thesystem.

For purposes of comparison with planned supercomputers, assume that thecore CPU is an 8 gigaflop (GF) equivalent Power PC™, MIPS™, or ARM™,machine that has been augmented for multitasking by with zero-overheadtask switching. As above, assume that there are multiple,special-purpose processors within each node such as the communicationsreceivers and the transmitter station that communicate with the main andauxiliary processors (FPUs, matrix processors, etc.) by accessing theDFI bus.

In summary, the main features of the node processor can be (1) thezero-overhead task switching multitasking technology allied with astate-of-the-art processor, (2) the DFI bus for intra-nodecommunications, (3) the DFI-enabled multiprocessing capability, (4) themultiple communication modules with their photo-diode receivers, and (3)the single, optical-transmitter module.

The 1000 Gigaflop Wafer

For the wafer to be an effective and functional element in a computersystem, or even a supercomputer in its own right, wafer-scaleintegration of the individual processor nodes should be achieved. Pastefforts have centered around wafer-scale bus architectures for linkingall processors together. The disadvantages of this approach are slowcommunication speed between processors due to the long bus structuresand the attendant high capacitance. Other approaches have attempted tocommunicate between nodes using various optical methods. A recentfavorite is to have n laser emitters and n laser receivers on each nodewhere n is the number of nodes on the wafer. This point-to-pointcommunication allows each node to talk individually and directly to anyother node.

By switching to a broadcast model where each node has a single emitterbut n receivers, the chip area required for communications isapproximately halved. More importantly, the communications traffichandled by each node in the case of a fully connected wafer can easilyoverload the computational capacity of the node itself for bothtransmission and reception. In the invention with the broadcast model,where each node has but a single emitter, the transmission load isapproximately n times less while the receiving communications load canbe maximal (the wafer can run with all nodes transmittingsimultaneously).

In addition to the optical-based broadcast mode of communications, eachnode on the wafer communicates with its nearest neighbors in the usualfashion. That is, each node has four data buses (north, south, east, andwest) so that the entire wafer is connected in a Manhattan grid. This“grid bus” not only provides an alternative path for messages but may beused for diagnostics as well as systolic-array applications.

Clearly, a communications protocol should be established to decidewhether a particular transmitted message is for a particular node sinceany given emitter talks to all nodes. If the nodes are indexed ornumbered for identification purposes, a map may be constructed for eachnode in the array. This map specifies which receiver on a given node isoptically linked to which particular emitter. Each receiver is thenmonitored by a circuit or task running on the node in question, thistask identifying messages for receiving node and ignoring all others.

Messages across the wafer are delayed only due to the finite speed oflight and the length of the modulation sequences. Present-day machinesrequires message passing or a means of relaying from node to node formessages to across an array of processors.

The wafer broadcast model also makes use of the data-flow model in thatthe material DFI bus is now replaced with light. Data is accepted by areceiver on a target node if that data packet is addressed to that node.This allows controlled point-to-point communications to be achievedwithin the broadcast model as well as broadcasting system-wideinformation from a single transmitter. Hierarchical control of aninter-wafer communications is then a matter of software rather thanspecialized hardware.

More than 256 dies of dimension 10 by 10 mm can fit on a 200 mm diameterwafer and over 600 such dies can fit on a 300 mm wafer (the area of the300 mm wafer is 2.25 times larger than a 200 mm wafer). Larger dies meanfewer nodes, of course, but more area for additional processors andsupport circuitry per node. This trade-off between the number and sizeof the nodes is a key variable in the design equation for tailoringsupercomputer installations for specific uses.

In summary, the features of the wafer module can be (1) its full,optical, global interconnect based on a designed optical interconnect;(2) local interconnect on an x-y (Manhattan) grid; and (3) one or moremodulated light emitters on each node.

The Teraflop Briefcase

A single 300 mm (12 inch) wafer with optics can fit into a space of 12inch by 12 inch by 4 inch plus room for access hardware (wires,connectors, etc.), housing and mechanical support, and auxiliaryhardware. With 2 to 8 GF nodes, the performance figure would be between1 and 4 teraflops (one teraflop is one thousand gigaflops) and dependson the silicon technology use. Such a package would fit nicely inside abriefcase and consume a few kilowatts of power, making a fully portabledevice (battery powered with a heavy-duty auxiliary battery pack).

Two wafers facing each other through a half-silvered mirror comprise afully connected system of 1024 processors. The nodes on wafer A can talkto each other by reflection from the mirror or talk to wafer B bytransmission through the half-silvered mirror; a similar situationobtains for wafer B with respect to wafer A. At 8 GF per node, theperformance figure for this configuration is approximately 8 teraflops.Power consumption would be between 1 and 100 KW depending on designparticulars (choice of silicon technology and clock speed). For thelow-power version, the cooling fluid could be a gas such as helium oreven air. In the high-power configuration, the can be bonded to aforce-cooled heat-sink, for instance a copper plate. The size of thepackage would be about that of a thick briefcase-about 12 inches by 15inches by about 8 inches thick. At a kilowatt, battery operation wouldrequire an auxiliary package; the faster versions (up to 8 teraflopswith present-day technology) would not support portable operation, butrequire external power and additional cooling in the form of a highheat-capacity fluid and a heat-exchange system.

A similar system based on multi-chip modules (MCMs) or printed-circuitboards (PCBs) having 10 optical communications nodes arranged as a 2 by5 array of optical communication nodes, with each communication nodesupporting four processing nodes (modules) each, and each processingnode (module) having quad 8 GF processors can be built today. Such adevice would also fit into a standard briefcase and consume about 1kilowatt of power and have a peak performance of over 1 teraflop.

In summary, a briefcase version of a teraflop supercomputer is not onlyconceivable but achievable with today's component technology. Trueportability depends on battery and cooling technologies and desiredauxiliaries such as storage, input, and output devices.

The 200 Teraflop File Cabinet

A convenient cabinet containing 300 mm wafers, optics, and cooling canbe about 0.5 m on a side by 1 m in length. Spaced at 20 cm apart, therecan be 50 such wafers in a cabinet, giving a total of approximately25,600 processor nodes in a cabinet. This is about twice the number ofprocessors in the AP 100-TF machine, yet, due to theoptical-interconnect feature, the invention can take up far less spaceand power. Wafer-to-wafer communication can also be by wire connectionsor SONET-like optical interconnects for those wafers not facing eachother.

Wafers, interconnects between wafers, cooling plates, and mountinghardware all contribute to the weight of the teraflop cabinet. Theestimated total weight is about 150 kg for a fully functional cabinet,excluding power supply and cooling.

In summary, the main features of the cabinet system can be its (1)mounting and cooling systems, (2) on-and off-cabinet fiber-opticcommunications, and (3) modularity of function and design.

The Petaflop Room

A small room containing 5 to a few dozen of the cabinets will provide acomputing power in the petaflop (PF) range. (A petaflop is one thousandteraflops or one million gigaflops.) Five cabinets, taking up a fewsquare meters of floor space, yield a 1 PF computer while two dozen suchcabinets in a single layer would require about 120 sq. ft. of floorspace, 5 megawatts of power, and result in a performance figure of about5 petaflops. In contrast, previously planned versions of a petaflopmachine are considerably larger and more power-hungry than the machineenvisioned here.

Interconnection between the cabinets can be by standard fiber-opticcommunications technology with transmitters and receivers integrated onthe wafers themselves. Multiple fibers between cabinets, with severalfibers between each wafer, can fully connect one stack of wafers toanother using the same zero-overhead-task switching and DFI technologiesas described above.

The Exaflop Suite

One quarter of a million wafers, 512 nodes per wafer, 8 GF per nodegives a 1 exaflop (EF) total performance figure. (An exaflop is onethousand petaflops, or one million teraflops, or one billion gigaflops.)A convenient cabinet, as discussed above, contains 50 wafers, meaningapproximately 5000 such cabinets in all, for a total volume of 1250 m³.Stacked three layers high to form 1.5 m high units, the floor spacecovered by these 5000 cabinets will be approximately 833 m² (excludingaccess corridors), or about the floor space of an office suite (lessthan 9000 sq. ft.). The interconnections can be optical (light beams)and contained in the spaces between the wafers along with the powergrids and cooling fluid as described above. Although such a machineoccupies an area equal to the ASCI Purple, it weighs 3 to 4 times more.However, the specific area and weight (per teraflop) is several thousandtimes less than ASCI Purple in area and several hundred times less inweight. This extreme contrast underscores that this new family ofsupercomputers can easily span the range from the portable to themassive using the same modular technology and zero-overhead-taskswitching based DFI interconnect.

The specific power consumption is about 30 kW/TF for AP and is about 2kW/TF for the invention, depending on the processor used. This isapproximately 15 times lower than AP and still considerably better thanBGL. However, the specific power density (watts per cubic meter perteraflop) of the invention is even more favorable, being less than onehundredth of that of the AP. The processing density of the invention,primarily due to the wafer-scale integration, is between 2 and 3 ordersof magnitude higher than AP. The total cost is expected to be about thesame to 10 times more for a full scale embodiment of the invention thanfor the AP, while the specific cost (in dollars per teraflop orprice-to-performance) is two to three orders of magnitude more favorablefor the invention than for the AP. This extreme contrast in specificpower and price performance underscores the essential affordability ofthe invention.

In summary, the main points of the inventive family of supercomputersare (1) wide scalability as evinced by the specific size, cost,capability, and power consumption, (2) modular construction; (3)inherently low cost, and (4) high reliability of opticalinterconnections.

Auxiliary Hardware

Optical Interconnect

A significant feature of the wafer-scale interconnect system is a lensarray that both spreads the light from each individual emitter andcollects this spread light, reflected from a plane mirror back onto thewafer, focusing light beams onto each of the individual photo-diodereceivers. The emitters themselves should be modulated light sources inthe form of gas plasma discharge devices, light-emitting diodes (LEDs)or solid-state lasers.

In the invention, light from each emitter illuminates the entire waferafter reflection from a mirror held parallel to the water surface. Acompound-lens array focuses this light on to each node. Since theemitters are varying distances from a given target node, the focalpoints at the target node are at different locations, effectivelyimaging the array of nodes onto each node in the array. An additionalmicrolens array can be placed just above each node so that the focusedlight from the main lens array is further concentrated on the individualreceiver photo-diodes distributed across each node.

Mass Storage & RAM

In addition to local memory at each node, each wafer may be serviced bya conventional RAID array or blade computer including a single CPU(perhaps the same processor as used on the wafer), mass storage andrandom-access memory as needed. Some configurations may require a singleRAID array or blade computer per cabinet, while others may need one ormore servers per wafer. A supercomputer used primarily as a video orimage server might require more mass storage than one configuredprimarily as a weather simulator, for example.

This marriage of the blade computer or RAID array with the wafer levelfree space fan out optical backplane interconnect concept dramaticallyincreases the flexibility of configuring a supercomputer out of standardcomponents yet tailored to specific applications. Interconnectionoptions could be built in to the modules, allowing a given installationto easily reconfigure its hardware to solve a wider range of problems asthe need arose. This is a variation on the scalability issue where onedesign tends to fit a very wide range of needs.

Communications

Connections to the outside world (console devices, other computers, thehigh-speed internet) can be by standard, off-the-shelf fiber opticsmodules and components. Indeed, each wafer or certain designated waferscan have integrally mounted optical modulators and demodulators for suchfiber communications.

Power Considerations

For the briefcase model, there will be 256 nodes per wafer running about5 Watts per node. Thus, a wafer will dissipate about 1.25 kW of power.Increasing this to 512 nodes per wafer and a power density approachingthat of the Power PC or Pentium™, (upwards of 100 W per node) means awafer will dissipate about 50 kW per wafer. With 50 wafers to a cabinet,65 kW should be removed for the low-end system and over 2.5 MW from thehigh-end system on a per-cabinet basis. Therefore, the space required bythe cooling system may be roughly the same as required by thewafer-containing cabinets.

This heat is distributed across each wafer and should be removed in sucha fashion as to keep the entire wafer at a uniform and reasonably lowtemperature. Two different approaches are suggested: (1) circulate acooling fluid throughout each cabinet such that each wafer is uniformlycooled and (2) mount each wafer or pair of wafers on a copper-alloycooling plate, each plate having a cooling fluid circulated to, throughand away from it. The cooling-plate solution has an additional advantageof forming a superstructure for precise mounting of the opticalcomponents.

Software

Operating System Software

This primary operating system for the invention can be Linux, configuredto handle multiple modes as ccNUMA capable processors executing a singleoperating-system image. A single Linux 2.6 image can be run on eachwafer, allowing 65,000 to 130,000 tasks under a single Linux image to bemanaged across a wafer. Optional operating system software supported caninclude packages capable of creating Beowulf clusters, a proventechnology for building supercomputers from clusters of Linuxworkstations.

Communications Software

Low overhead communication between nodes can be implemented using theemitter-receiver optical technology outlined previously. This technologycan underlie the ccNuma implementation, and may be exposed for use byprogramming libraries (e.g., MPI), or for direct usage by bespokeapplications.

Compilers

The inventive system can provide standard compilers for languages suchas C, C++, Java, etc. For scientific computing, languages like HPF,Fortran90, and Fortran77 can be supported, as can extended versions of Cand C++. The invention can include compilers that can generate code tothe particular strengths of the inventive architecture, includingoptimization to map intermediate representations of dataflow to the finegrained zero-overhead-task switching multitasking.

Programming Libraries

Various portable supercomputing libraries, such as OpenMP, MPI, and PVM,can provide portable programming APIs for supercomputer applications.

System Management

When very large machines are built, supercomputers or otherwise, thereis a requirement for system management packages. For the invention,there can be packages for system backup, system volume management,hardware fault detection and isolation, resource allocation, and systempartitioning.

Multitasking and Hypertasking

The invention can include zero-overhead task switching (e.g., ZOTS™) andthe hardware methods for managing a multitasking system based ondynamically changing task priorities and round-robin schedulingdisclosed in U.S. Ser. No. 10/227,050, filed Aug. 23, 2002. Embodimentsof hardware methods for managing a multitasking system based ondynamically changing task priorities and round-robin schedulingdescribed in U.S. Ser. No. 10/175,621, filed Jun. 20, 2002 are readilycommercially available from Xyron Corporation and/or LightFleetCorporation, both of these companies having offices in Vancouver, Wash.,USA, and one or both of these companies are identified as the source ofthese embodiments by the trademark hwRTOS™, but the invention is notlimited to a hardware method for managing a multitasking system based ondynamically changing task priorities and round-robin scheduling, muchless these hwRTOS™ embodiments. A hardware, real-time operating systemmay be thought of as an essential kernel of a real-time operating system(RTOS) embodied in hardware. The combination of zero-overhead-taskswitching and hardware methods for managing a multitasking system basedon dynamically changing task priorities and round-robin scheduling,enables on-chip multitasking to be performed with optimal efficiencysuch that all CPU cycles are applied to the computational task and nonewasted on management overhead functions. Potential costs of someembodiments of the invention are latencies associated with prioritymanagement and silicon area required for the circuitry. The former istypically a few gate delays while the latter scales as n In n tasks.These costs remain negligible for up to 512 tasks per node, meaning thatthe benefits of fine-grained multitasking are achievable for a widerange of applications for very little cost.

The same multitasking idea manages communications and messages betweennodes on a wafer and between wafers. At the wafer scale, hardwaremethods for managing a multitasking system based on dynamically changingtask priorities and round-robin scheduling, residing on each node meanshundreds of thousands of individual tasks across the system areavailable for fine-grained decomposition of difficult problems; the term“hypertasking” distinguishes this pan-wafer task management andswitching from on-chip multitasking. In a supercomputer configuration,many of these tasks, to be sure, will be dedicated to handling themyriad messages that must crisscross the wafer, but a substantialportion will be available to the programmer, allowing greatercomputational efficiency than presently achievable. For example, certainsupervisory nodes on each wafer will be responsible for multitaskdecomposition of code fragments. These supervisors then distribute themultiple tasks across the wafer or the entire system as necessary.Interplay between various nodes concerning issues of priority,scheduling, and task completion communicated by the optical backplane tosupervisory nodes form the logical basis behind hypertasking, which maybe thought of as distributed but inter-coordinated multitasking.

Hypertasking allows the effective degree of parallelism to besignificantly higher than previous computational models once theinterplay between software and the hardware-enabled multitasking areunderstood and used to advantage.

Data Flow Interface

The data flow interface (DFI) architecture allows multiple processors,some of which can be small and dedicated, to reside on a single nodewhile retaining effective and efficient data pathways between thefunctional parts. Imagine an asynchronous, high-speed bus connecting theCPU, multiple FPUs, math coprocessors such as multiply and accumulatesor MACs, communications-stack processors, and other functional units.Enough local intelligence resides in the DFI to achieve dynamic routingof data packets, allowing control messages and data to directly reachdestinations without traveling over circuitous paths. This flow ismanaged locally within the DFI, freeing the CPU for more useful work.Local control means that specialized hardware modules typically used forDMA and bus control, so essential in conventional architectures, are notrequired in DFI-based zero-overhead-task switching machines.

It is envisioned that each photodiode receiver station will reside onsuch a data path and be managed by a local task or stack processor.Since the communications system operates in broadcast mode, mostmessages received at a given station will probably be meant for anothernode. Local processing of data packets ensures that messages will notcollide nor delay one another even though all nodes may besimultaneously broadcasting information. Messages not meant for thereceiving node are simply ignored; as such they do not contribute to DFItraffic within that node.

Optical Backplane

What is not often realized, is that the synchronization and coordinationbetween the set of receivers and set of emitters is also a verydifficult problem when fine-grained multitasking should be avoided. Itis important to appreciate that the two problems of point-to-pointconnectivity and message synchronization are solved by a broadcast modelcoupled with the zero-overhead-task switching and DFI techniques.

A fully connected wafer of processors has never been attempted. Such atask involves a nightmare topology of interconnect busses andbus-arbitration devices. Any implementation would involve multiple metallayers and require enough wafer area as to lower the processor density.The only practical approach to full and direct interconnect is optical.The invention can include a broadcast model where each node has oneemitter that is optically connected to all other nodes on the wafer. Alenslet placed above each emitter forms a shaped light beam before thebeam reaches the diverging element residing in the main compound-lensarray. As explained above (Optical Interconnect), a compound lens arrayis placed between the wafer and a mirror. This array both spreads thelight from each emitter so that it illuminates the entire wafer uponreflection and focuses light onto each node's receiver array. Anadditional n×n lenslet array can sit atop each node to adjust the focusof the main, compound-lens array onto each of the photodiode n²receivers on each node. These several lens arrays may be opticalholograms, cast optical elements, or assembled from individual lenses.

The zero-overhead-task switching approach addresses the problem ofmessage synchronization by replacing issues of strict communicationcoherency with fine-grained tasks that allow asynchronous messaged toflow from node to node. The broadcast concept allows messages to crossan entire wafer in a single step whereas the point-to-point opticalinterconnect requires nearly twice as much hardware to accomplish thesame result and introduces message delays due to the relaying process.

Parallelism Issues

A good way to finesse Amdahl's law has not yet been found. Since theserial portion of a calculation dominates the time to perform thecalculation as the number of processors increase (Amdahl's law), oneshould redefine the serial portion so that it may be more effectivelyexecuted. While respecting the serial nature of a given problem, it ispossible, in many cases, to speed up any sequence of serial steps bymeans of multithreading. The zero-overhead-task switching architecturewith its priority-based task scheduling forms the basis for afine-grained superset of multithreading, yielding a substantial speedimprovement over simple, high-level multithreading. The result is aneffective way to circumvent Amdahl's law since an erstwhile serialportion of code, if written at a sufficiently abstract level (removedfrom hardware), can be decomposed into a large number of small tasksthat have little or no dependencies. The result is an apparentparallelism of a serial section of code in that the processor executingthis code runs at greatly enhanced efficiency due to removal of memoryand data-access latencies achieved by hardware-controlled inter-taskreshuffling.

In carrying this latter idea across processing nodes (modules), it iseasy to see that the zero-overhead-task switching concept enablesparallel algorithms to perform at their optimum. First, decomposing agiven problem into a set of parallel and serial portions allows eachportion to be efficiently mapped onto a set of fine-grained tasks whichare then managed and coordinated by the hardware task manager across aset of nodes and executed with little to no overhead by thezero-overhead-task switching mechanism. Second, hardware multitaskingavoids latency associated with message passing and communicationsbetween parallel tasks. This, in turn, alleviates the problem associatedwith inter-node data dependencies in the same fashion as above.

The zero-overhead-task switching and hardware methods for managing amultitasking system based on dynamically changing task priorities andround-robin scheduling, mechanisms allow efficient and effective use ofmultitasking within nodes and hypertasking across a network of nodes.The result is lower latency, a method of handling data dependencies, andmore effective use of all processors in the system. Additionally,auxiliary hardware found in conventional supercomputers fordirect-memory access, bus hardware and controllers, cross-bar mechanismsand controllers, system broadcast modules, and the like are simply notneeded since the functions performed by the specialized hardware listedabove are effectively performed as software tasks in a priority-managedsystem based on zero-overhead-task switching and hardware methods formanaging a multitasking system based on dynamically changing taskpriorities and round-robin scheduling. The absence of the suite ofcommunications hardware greatly reduces the need for complicatedcommunications software.

The broadcast model coupled with the compound lens array means highertolerance to mechanical misalignment, eliminates the need of strictcoordination between messages, and achieves faster communications atlower power and cost. Material busses and cross bars are eliminatedmeaning that less hardware and power dissipation are required; theresult is lower overall system cost.

The combination of these technologies, innovations and off-the-shelfcomponents results in a scalable, modular supercomputer system thattakes advantages of economies of scale and allows dynamicreconfigurability far beyond that of present and planned machines.

Thermal Considerations

Commercial off-the-shelf MMC (metal matrix ceramic) such as copper withpitch based graphite can be matched to the coefficient of thermalexpansion of silicon and conduct heat away from the circuits and towarda heat sink. The invention can also utilize a gold eutectic bonded tothe circuits or wafer. In addition, the wafer can be thinned ifnecessary. The invention could include the use of a wafer made from puresilicon-28 isotope which has a 60% improved thermal conductivity.Preferred embodiments of the invention can operation at temperatures offrom −50 to 25 C., held to within 1 degree. Based on a calculatedthermal differential for a 200 um thick silicon wafer at 5 kWdissipation and 1 degree C. estimates a cost of approximately $1000 per5 kW wafer for a chiller.

A more complicated version of the invention can include a clear coolingbath placed on the front side of the wafer as well. In that case, if gasplasma discharge devices were used as the signal emitters the gasdischarge cells could include roughly 2 mm diameter microspheres filledwith an appropriate gas at the appropriate pressure.

Power Supply

The need for 5 KW at 1.5V and 4000 A is non-trivial. Preferredembodiments of the invention can include a full 3-phase solution at 400VAC in a standard “Y” configuration. Unisolated direct PWM buckconverter to 1.5V. Multiple stages may be used if necessary, but themain point for cost is to avoid the use of active transistors or diodesat the 1.5 voltage level. The final filtering can be done with smallpassive inductors and capacitors (using a 1 MHz switching frequency).Isolation is desirable, albeit at added cost and weight, and should bedone in the first stage, by converting the 400 VAC to 48-120 VDC.Calculations indicate that the power supplies can be about the size ofthe PC power supply for each wafer. Of course, the invention can useconventional off the shelf power supplies.

To minimize writing losses at the low voltages, the power suppliesshould be mounted within a foot or so of the wafer. A 1 cm (0000′ gauge)copier wire can go from the power supply to the copper graphite MMCwafer TCE matched xy power grid. To provide a large amount of bypasscapacitance, barium titanate dielectric or other high capacitancematerial can be integrated into the power plates. Dead and shorted nodescan be removed via laser. Wafers with too many bad nodes, can be cut upand used as standard IC's.

Mechanical

Matching thermal coefficients of expansion is important to reliableoperations. Pitch derived graphite in a copper or A1 matrix, can bematched to any thermal coefficients of expansion from the base metalcoefficients to −0.002 ppm/K.

Optical alignment requirements are in the 0.3 mrad or about 100 micronsvertical edge to edge for a 12 inch wafer. In view of the fact that theinvention can include cooling and controlling the temperature of theentire assembly, there will be no trouble achieving the opticalalignment needed. For instance, the invention can be embodied in an 8inch high by 13 inch square processing box, with a half inch IDinsulated cold liquid input and an uninsulated half inch ID output tubegoing to a chiller.

Mounting of conventional off the shelf laser die and IR receivers can beimplemented using standard pick and place systems. The invention caninclude the use of standard IC process wire bonding pads to easealignment requirements. For example, silver filled epoxy has enoughflexibility to accommodate the TCE differences inherent in theseconnections.

Testing

The high speed integrated optical receivers can be testing using a smallsolid state laser attached to a testing head that uses the broadcastmode to illuminate all 512 photodiodes at once while probing the waferto insure that all receivers work. Many companies including Agilent makeoptical testing heads, so they are readily commercially available.

Pick-and-Place of Optoelectronic Die on Wafer

The invention can including pick and place of a chip onto a 12 inchwafer with 30 micron xy accuracy and the inclusion of a precision dropof conductive silver adhesive. Equipment that can place within +5microns is readily commercially available.

Optical Interconnect Layer

As previously discussed, it has long been recognized that electricalinterconnect methods are approaching their limit in spite of advances inphoto-lithography and the miniaturization of high-speed electrical delaylines. Another way of viewing the situation is that electricalinterconnects are reaching a limit whereas free-space opticalinterconnects continue to scale according to an optical Moore's Lawdependent on the information capacity of modulated light and theachievable density of photoreceivers. The inherent advantages of opticsrests on the non-interference of light in free space. While fiber opticsretains some of the disadvantages of electrical delay lines, namely thephysical space occupied by the fibers or electrical wiring, free-spaceoptical communication has no such disadvantage.

The invention overcomes most all of the problems and difficulties ofpresent approaches to FSOI by making simultaneous use of two keyconcepts, that of optical fan-out and broadcast. Both of these conceptshave been widely recognized as enabling ideas for FSOI, however theyhave yet to be combined into a unified approach. The novel lensstructure disclosed here allows both fan-out and broadcast to becombined in a simple and inexpensive yet powerful FSOI.

The invention provides a way of fully interconnecting a plurality ofassociated circuit modules lying in a plane or other geometricconfiguration. Conceptually and functionally, the circuit modules aregrouped into heterogeneous functional sets, which may be termed a nodeor processing node or processing module, whether or not the set performscomputations in the sense of a computer. A multiprocessing system caninclude a number of processing nodes linked by either electrical oroptical connections, or a combination of the two. The invention can bebased on a free-space optical interconnect (FSOI) between multiplenodes. Associated with each node are one or more emitters (transmitters)and one or more detectors (receivers). If there are n communicatingnodes in a system, there can be n emitters and n(n−1) receivers, or n(n)receivers if desired. Each emitter broadcasts information via opticalfan-out to all other n−1 nodes in the system. Each node also has areceiver for each of the other n−1 nodes in the system (or for n nodesby allowing each node to communicate with itself, in which case theinformation is broadcast to all n nodes in the system). The mapping ofthe entire set of n emitters to the receivers within a single node isone-to-one so that the simple presence of a message at a receiverautomatically identifies the emitter or source of the message. However,since each emitter is broadcasting to all of its receivers when sendinga message, the desired destination of a message may be ambiguous. Thatis, a given message might be meant for all nodes in the system, aparticular subgroup of nodes, or a single particular node. Thisambiguity can be resolved by supplying each message with a short headerthat identifies the intended recipient. This message header may bedecoded by circuitry located at the receiver site. A message for aparticular receiver will then be passed on to a subsequent stage ofprocessing. Any message not intended for a particular receiving node issimply ignored. Message contention or collision is not an issue in theinterconnect described herein.

Optionally, there can be one or more modules associated with each node.If there are two or more modules associated with a node and two or moreemitters associated with that node, then each of those emitters can beassociated with one, or two (or more) of those modules. (If there isonly one emitter associated with a node, it can be associated with allthe modules associated with that node.) For instance, if there are fourlaser diode emitters associated with a node and four computationalprocessing modules associated with that node, then each of thecomputational modules may have a one-to-one association with one of thediode emitters. Further, each of the optical signal detectors associatedwith that (multi-module associated) node then needs to query not merelywhether an incoming received data signal is addressed to that node, butwhether and to which of the four associated modules that incoming datasignal is addressed.

This new broadcast capability should lead to substantial performancegains as a percentage of peak performance. The broadcast method derivedfrom the invention is a simultaneous non-blocking broadcast capabilityfor short messages. While the 8-byte bandwidth provided by the inventionis already over 100 times higher than in competing systems, the peakbroadcast bandwidth is a multiple, by the number of communication nodes,beyond. For a 64-communications-node system, this translates into a peakbroadcast bandwidth of over 7 gigabytes per second per communicationsand a peak bisection broadcast bandwidth of 448 gigabytes per second,all based on commercial Sonet OC48 electro-optical components operatingat 2.5 gigabits per second. This unexpectedly advantageous result is dueto the ability of all 64 laser transmitters to optically broadcast toall receiving nodes where each individual receiver or pixel(s) has anassociated short-message buffer.

Optical Fan-Out & Broadcast

The invention has been reduced to practice and demonstratesinterconnecting large numbers of processing elements within a smallvolume. The invention makes use of optical fan-out wherein a singlelight emitter can broadcast its signal to multiple receivers. Although agiven emitter can broadcast to multiple receivers efficiently andeffectively, a single receiver should not receive information from morethan a single emitter, otherwise message contention as well as confusionof origin can arise. Electrically, this fan-out function would beachieved by an electrical fan-out or multiplexing circuit, oftenreferred to as an electrical cross bar, along with buffer amplifiers foreach pathway from a given emitting node. Optically, a simple way toaccomplish fan-out is by spreading the output of an emitter with anoptical element and then refocusing portions of the fanned-out beam withmultiple collecting lenses. Since a broadcast message reaches allreceiving nodes in the system nearly simultaneously, a destination codeis required to identify the desired recipient or recipients of thetransmitted message; such a code is necessary for broadcasting messagesboth electrically and optically.

FIG. 17 illustrates the concept of optical fan-out. The broadcastapproach disclosed herein is both simultaneous (to all nodes in thesystem at the same time) and non-blocking (multiple nodes maysimultaneously broadcast information). In this document, “broadcast”will be taken to mean “simultaneous, non-blocking broadcast” unlessstated otherwise.

Referring to FIG. 17, fan-out (divergence) from a light source isdepicted. The light source 1710 is represented by the circle at the leftof the figure. The shaded triangle with apex at the light sourcerepresents the inherent spread or divergence of the light beam from thelight source. The light source (emitter) can be one, or more than one,optical signal emitter(s). The optical signal emitter can be gas plasmadischarge optical signal emitter, a light emitting diode and/or a laserdiode or any other signal emitting capable light source. In the case ofmore than one emitter, the plurality of emitters can define a cluster ofoptical signal emitters. The cluster can include emitters that operateon different frequencies to enable frequency (wavelength or color)multiplexing and/or emitters that operate on substantially the samefrequency to enable parallel output power aggregation. (Similarly, thelight receiver (detector), described elsewhere in more detail, candefine a cluster of receivers, of the same or different types.)Throughput this document, when the terms emitter or receiver (or theirequivalents) are recited, the corresponding clusters that can be definedare deemed to also be described.

Still referring to FIG. 17, a spreading element 1720 can increase thefan-out of the original light beam to cover an entire set of collectionand focusing optics that are described elsewhere and shown in otherfigures. The spreading element 1720 can be one, or more than one, lensor any other light diverging capable optical spreading structure. Thespreading element 1720 can include a concave lens, a concave-concavelens and/or a convex-concave lens. The spreading element can include aFresnel lens. The spreading element can include a holographic element.

Light from each emitter in the interconnect can undergo an initialoptical fan-out by integral optics that are coupled to the emitter(s),such as a spreading and shaping lens commonly packaged with one or moregas plasma discharge emitters, lasers or light-emitting diodes (LEDs).Further, the integrated optic and emitter can be integral with thecircuit(s) that provide the signal and/or the power to the emitter(s).In the invention, fan-out can be increased as needed through the use ofone or more optic(s) placed in line with the emitter and preferablylying substantially in the plane of the light-collecting optics. (Theselight-collecting optical elements will be described in more detail in asubsequent section.)

Once the light from an emitter is sufficiently spread out so as to coveror illuminate an entire set of receiving elements, or at least a subsetof the receiving elements, the light should then be sufficientlyconcentrated so that individual receiving elements (e.g.,photoreceivers) will have sufficient intensity to allow detection of thesignal being broadcast. If the originating light beam is sufficientlypowerful, then no additional concentrating element is required. Such anarrangement is practical only for broadcast to a set of receivers lyingwithin a small area. The larger this receiving region, the more powerfulthe light source should be to supply sufficient power to each detector(e.g., photoreceiver).

The invention overcomes the problems of inadequate light intensity atthe receivers as well as the problem of maintaining precise alignment ofthe emitter beam with the receiver position by a novel configuration ofdiverging and converging optics. In contrast to the usual approach tothe FSOI problem, maintaining a precise direction of the emitter beam isno longer a critical parameter. In the invention, a critical parameterbecomes the position of the emitter with respect to the set ofreceivers; something that is relatively easy to achieve inprinted-circuit boards (PCBs) and multi-chip modules (MCMs). Thelithographic processes presently used in fabrication of siliconmicro-electronics are at least an order of magnitude more precise thanneeded to achieve the accuracy that is required for the invention. Thus,the constraint on beam direction in point-to-point systems is replacedby the easier-to-achieve positional constraint provided by theinvention.

Registration of the image of the array of emitters with each receiverarray depends on the placement and design of a lens structure above eachreceiver array. The constraint on the placement of this structure isprimarily lateral in nature and should be met to within a fraction ofthe receiver spacing, something that is again relatively easy to achieveusing mounting posts or stand-offs precisely located on the PCB or MCM.All location and angle tolerances in the system disclosed herein areroughly multiplied by the optical power of the lens structure. Forexample, if an array of emitters of linear dimension d is focused ontoan array of receivers of linear dimension r by the system optics, alinear tolerance of t mm becomes t d/r mm, where d/r is typicallypreferably approximately 10 or greater. Thus, if the constraint is tomaintain beam focus on a receiver to within 50 microns, the placement ofthe lenses or mounting posts or other elements should collectivelycontribute no more than 0.5 mm to the misalignment. This is a tolerancethat is quite easy to achieve.

Referring to FIG. 18, a form of optical multiplexing is enabled withoutthe need for multiple amplifiers or buffers as in the case of anelectrical multiplexer or fiber-optic star multiplexer. FIG. 18illustrates how information from a single emitter can be broadcast tomultiple receivers using a set of light-collecting and focusing (e.g.,converging) elements.

FIG. 18 illustrates optical broadcast from a single emitter located atthe apex of the cone of light on the left of the figure, representing anembodiment of the invention. The light from this single emitter has beenfanned-out by appropriate optics not shown in this figure (e.g., adiverging concave-concave Fresnel lens). An array of light-collectingand focusing optics 1810 is represented by the column of ovals shown onthe right side of the figure. Each element 1820 of the light-collectingand focusing optics 1810 can be one, or more than one, lens or any otherlight converging and focusing capable optical spreading structure. Thelight-collecting and focusing elements 1820 can include a convex lens, aconcave-convex lens and/or a convex-convex lens. The light-collectingand focusing elements 1820 can include a Fresnel lens.

Fanned-out light incident on each collecting optic can be focused onto aphotoreceiver located at the apex 1830 of the light cones to the rightof the optic array. Thus, light from a single emitter is made availableto multiple receivers through the use of fan-out with the result thatinformation contained in the light is broadcast to all receivers thatlie at an appropriate focal point of the collecting optics. It can beappreciated that the receivers can be located in a coplanar arrangement.Any particular receiver can ignore a message by examining a code (e.g.,header in a broadcast packet) designed to specify message destination,and determining that the message is ear-marked for another node. Thecombination of the fan-out and multiplexing nature of the exemplary lensstructure disclosed in this document comprises a particular approach ofachieving a fully interconnected, broadcast, optical-interconnect systemand the invention is of course not limited to the described examples.

Optical Interconnect

The invention significantly avoids joining and splitting problemsassociated with confined light beams as in light pipes or fiber optics.Moreover, the invention significantly avoids the more severe problemsassociated with electrical interconnects and point-to-point FSOImethods.

Referring to FIG. 19, a set of three emitters A, B, C are located on theleft side and a set of receivers are located on the right side of theillustration. FIG. 19 illustrates the concept of broadcasting opticalinformation from a plurality of emitters to a plurality of receivers.All three of the fanned-out signals from emitters A, B, C are collectedand focused by the set of light collecting and focusing optics 1910. Itis important to appreciate that FIG. 19 represents an “unfolded”configuration wherein the emitters and receivers lie in differentplanes. It is possible, and it is a preferred embodiment of theinvention, to employ a folded configuration wherein a mirror is placedsubstantially parallel to a plane containing both the emitters and thereceivers. FIG. 19 can adequately represent a folded configuration bysimply imaging the mirror to lie precisely halfway between the emitterplane on the left and the receiver plane on the right, with itsreflective side towards the emitter-receiver array. In thisinterpretation of the graphic, the illustration has been unfolded, notthe device itself and the receiver array on the right is the mirrorimage of the actual receivers which lie in the plane of emitters on theleft. Please note that the sequence of A, B, C on the left from top tobottom is reversed to c, b, a on the right from top to bottom,consistent with a (reversed) mirror image. Where convenient, an unfoldedgraphic will be used to illustrate both folded and unfoldedconfigurations of the optical interconnect.

Referring to FIG. 19, fan-out from multiple sources falling on the sameset of collecting and focusing optics 1910 is depicted. This opticalmultiplexing establishes an optical fabric that connects n sources ton×m receivers in broadcast mode, where there are m receiver arrays inthe system (n need not equal m). Each emitter is labeled by anupper-case letter (A,B,C) on the left. Each of the set of receiverarrays 1940 on the right (7 are depicted in FIG. 19) receives light fromeach of the three emitters. The individual receivers are labeled bylower-case letters (c,b,a). Since light from mutually incoherent sourcesdoes not interfere at an optical element and light from differentsources does not interfere in free space, light reaching a particularreceiver, say any of the a receivers, originates only at a singleemitter (A in this case).

The mirror element (not shown in FIG. 19) need not be a specularlyreflecting device such as a first-surface, metalized glass substrate. Itis possible to replace the mirror with a diffuse reflector as found in amovie or projector screen. In this screen implementation, the light fromthe emitters is not spread out, but kept in narrowly focused beams. Thearray of beams then impacts the screen in a precise grid of points. Eachbeam then undergoes a diffuse reflection from the screen and illuminatesthe entire array of collecting lenses. More light is lost in thisapproach than in a specular reflection from a metalized mirror, so theemitters should be correspondingly brighter. Alignment is more difficultin this case as each emitted beam should be directed precisely onto alocation on the screen to within an accuracy that is approximately halfthe size of the active portion of a receiver (usually a few hundredmicrons or smaller) multiplied by the optical power as explained above.The angular constraint on the parallelism of the plane of the screenwith the plane of the receivers remains as before, but the overalleffect of an optical broadcast interconnect is achievable.

The arrangement of emitters, receivers, lenses, and mirror or screenform the optical backplane or fabric that interconnects each processornode optically to every other processor node in the computing cluster.The fundamental concepts that allow this interconnect method to functioneffectively and efficiently are the aforementioned optical fan-out andoptical broadcast. This document discloses several methods to achieveeffective optical coupling between emitter and receiver stations.

The Preferred Lens Structure

A goal of the invention is to provide a method of optically imaging anarray of emitters onto multiple arrays of receivers. Each receiver arrayshould lie in the image plane of an optic that views the entire emitterarray. A single node or group of nodes or circuit modules communicatingwith a receiver array lying in the focal plane of a single collectinglens, including the receiver array, the collecting lens and any requiredoptics for spreading the output from one or more emitters can be termeda lightnode. The lens structure associated with a lightnode both spreadsout the light from the emitter so as to illuminate the entire array ofnodes and images light from all emitters in the system onto theparticular receiver array of that lightnode.

Typically, a node has one emitter for each processor node (module),although this is not a required constraint as processing nodes (modules)can have more than one light emitter each, or may well share lightemitters by temporal multiplexing. The receiver array belonging to alightnode may belong to a single processing node (module) or be sharedamong a group of processing nodes (modules) that may be associated withthe particular lightnode.

In one embodiment of the invention, each node has an associated emitterand an associated receiver array. Any of a variety of configurations arepossible under the constraint that each receiver array is configured asan image of the entire array of emitters. Two possible emitter andreceiver configurations are shown in FIGS. 20A and 20B.

Referring to FIGS. 20A and 20B, two of many possible configurations forthe front surface of a node having but a single emitter are depicted.The single emitter is shown as the open circle and the receivers as thearray of black dots centered in the larger square, which represents theboundary of the face of the node. The corresponding lens structure (notshown) lies above the plane of the page.

In both FIGS. 20A and 20B, the receiver array is centered in the nodeface. FIG. 20A shows the node's emitter 2010 above and to the left ofthe receiver array 2000. Here, the lower-right receiver 2015 in the nodereceives light from that node's emitter. In the node face layer depictedin FIG. 20B, the emitter 2020 is placed in the center of the receiverarray 2030. The image formed by the node's lens structure maps its ownemitter's light back onto the emitter 2020, however this causes noproblems since this particular light path is not focused by thecollecting optic that lies directly above the emitter, but spread twiceby the diverging optic. This action also occurs in FIG. 20A, but thecentral ray from the emitter 2010 to the mirror and back through thecenter of the collecting optic, which is centered above the receiverarray, actually reaches the receiver 2015 on the lower right.

Although a node can contain any number of emitters and processing nodes(modules), practical considerations usually limit this number to 1 or 4or 8. The larger the number, the more processing nodes (modules) arerequired to receive information from each receiver in a node. At somepoint, the electrical fan-out circuitry connecting multiple circuitmodules to a single receiver becomes unwieldy. Several configurationsare illustrated in FIGS. 21A-21C

Referring to FIGS. 21A-21C, three preferred embodiments of node facesare depicted. The large, open circles represent emitters and the arraysdots represent the receiver arrays. The embodiment depicted in FIG. 21Ahas an emitter multiplicity of 1, and shows a single emitter 2110 andits associated receiver array 2120. It can be appreciated from the 5×5configuration of the members of the receiver array 2120 that this nodeis configured for deployment as part of an array of 25 nodes. If theemitter 2110 is shared by more than one module, than each of thereceivers in the receiver array 2120 will need to determine if anincoming signal is for any of the more than one modules. The embodimentdepicted in FIG. 21B has an emitter multiplicity of 4 and is a morepreferred embodiment of a node configuration. Four emitters 2131, 2132,2133, 2134 are located outboard the corners of the receiver array 2140.It can be appreciated from the 6×6 configuration of the members of thereceiver array 2140 that this node is configured for deployment as partof an array of 9 nodes. If each of the four emitters 2131, 2132, 2133,2134 is associated with one of four modules, than each of the receiversin the receiver array 2140 will need to determine if an incoming signalis for any of the four modules. The embodiment depicted in FIG. 21C, hasan emitter multiplicity 8. The eight emitters 2150 are located in aspaced apart relationship around the perimeter of the receiver array2160. It can be appreciated from the configuration of the members of thereceiver array 2160 that this node is configured for deployment as partof an array of 4 nodes. If each of the eight emitters 2150 is associatedwith one of eight modules, than each of the receivers in the receiverarray 2160 will need to determine if an incoming signal is for any ofthe eight modules. Each of these three arrangements may be repeated inan array of nodes where the spacing of emitters in such an array hasregular and uniform spacing so that the image of the emitters is aregular array of focal points that is set to match any of the receiverarrays in the system.

In a more preferred embodiment of the invention, each node has amultiplicity of 4 meaning that there are 4 emitters associated with eachnode. These emitters can be spaced as shown FIG. 21B. The spacing shownallows a square array, for example, of nodes to be assembled where thespacing between emitters is the same across the array in both verticaland horizontal directions. The face of the nodes can be square, thisbeing a most convenient form, but the invention is not limited to squareface nodes.

The advantages of a multiplicity-4 array of nodes over an array having asingle emitter per node is that there is 4 times the light intensity perunit area for a given sized array and 75% fewer receivers in the entiresystem. The overall system size depends, among other factors, on thephysical dimensions of the receivers. Thus, a multiplicity-4 array ofnodes can occupy roughly 75% less area than a multiplicity-1 array.Although there are also 75% fewer lens structures, these structures(optics) are typically larger since the each now contains 4 fan-outelements. On the other hand, keeping the mirror close to thereceiver-emitter plane so as to limit the physical dimensions of theinterconnect then requires lens elements with larger numericalapertures.

An important element of the optical interconnect can be a lens structurethat effects simultaneously the fan-out of individual emitters toachieve broadcast of messages and the spatial de-multiplexing ofintermingled messages carried in the various light beams onto thevarious receiver arrays as illustrated in FIG. 19. Since light from theplane of emitters is focused on the plane of receivers, which lies asclose to the emitter plane (or, equivalently, the folding mirror liesclose to the plane containing both emitters and receivers), the optimallens design for imaging the emitters onto a receiver array should bedesigned with finite conjugate focal lengths as illustrated in FIG. 22.

Referring to FIG. 22, conjugate focal lengths defined by the convergingelement of an optic are depicted. In a typical lens, the focal length,f₁ is at infinity (for a parallel beam of light), while f₂ is 50 mm in atypical camera. For an exemplary converging element 2210 for use in anoptic of a lightnode, f₁ is the distance from the emitter 2220 to thelens and f₂ is the distance from the lens to the receiver 2230. Thesedistances may be quite different depending on the inherent spread in theemitter 2220 and the optic required to adjust this spread.

Each lightnode can have an associated focusing lens as illustrated inFIG. 22. Light from all emitters in the array of nodes falls on thelens, which is idealized as the shaded region to the left in FIG. 22.The function of the lens is to focus all incident light onto a receiver2230 in the face of the node; this is represented as the shaded regionto the right of FIG. 22, where the receiver 2230 in question lies at theapex of the shaded region on the far right. In a preferred embodiment,this collecting and focusing optic can be an aspheric, Fresnel lens withconjugate focal lengths that match the dimensions chosen for the opticalinterconnect system.

Since the set of emitters on the face of a node should illuminate theentire node array and the collecting and focusing lens should be asefficient as possible so as to reduce the requirement for optical powerof each emitter in the system, the diverging light from the emitters andthe converging light to the receivers should pass through the sameoptical system. This presents an inconsistency since any convergingelement will focus light incident from either side of that element. Thesolution to this dilemma is to place a “spreading aperture” in theconverging lens to allow light from an emitter to pass through theregion of the converging lens without being focused. If the inherentdivergence of an emitter allows light to reach the entire array of nodesand is not so great as to demand a large aperture through the collectingoptic, a simple hole in the collecting optic will suffice. It is usuallythe case, however, that the light emitted from the devices mostconvenient for the implementation of the invention emerges within afairly narrow cone of a few degrees, and with an oval cross section.Compensating optics can be placed at the emitter and produce a circularspreading beam of a few degrees. When this beam reaches the position ofthe lens structure, it may be a few mm in diameter. Allowing it tospread to cover the entire array of nodes usually requires a distancemany times larger than practical. In this case, the spreading aperturecan contain a small diverging lens that may also correct for anelliptically shaped beam should that be necessary. A multiplicity-4,Fresnel lens structure is illustrated in FIGS. 23A-23B.

Referring to FIGS. 23A-23B, a compound lens structure 2300 for a singlelightnode (module) servicing four processing nodes (modules) isdepicted. FIG. 23A is a top view of a Fresnel lens structure designed tospread out four emitter beams using four Fresnel lenses 2311, 2312,2313, 2314 which are depicted as the four smaller sets of concentriccircles. The light-collection portion 2320 of a lens structure caninclude a square section of a large-diameter compound aspheric Fresnellens or a smaller-diameter Fresnel lens lying within a square. Thedimensions of the square match those of the surface of the node face foroptimum light-gathering efficiency. FIG. 23B shows a cross section ofthe compound Fresnel lens structure 2300. A multiplicity-I lensstructure to match the structure depicted in FIG. 20A would have thethree small Fresnel lenses depicted in FIG. 23A (upper left 2311, lowerright 2313, and lower left 2314) removed with the grooves of the largelens continuing into those regions.

The light-collection part of a lightnode's lens structure is generallyany structure capable of gathering and focusing light such as sphericallenses, aspheric lenses, diffractive elements (binary optics andholograms), light funnels, and so on. A particular embodiment is can bean aspheric, compound Fresnel lens specifically designed with twodifferent conjugate focal lengths as shown in FIGS. 23A-23B. The overalldesign constraints are to minimize the volume occupied by the light(determined by the area of the lens structure and the sum of itsconjugate focal lengths) while allowing an optimal size for the array ofreceiver elements (receivers should be placed far enough apart tominimize or reduce cross talk between focal points and should be placedclose enough to ensure that the array fits within the desired area onthe face of a node).

Aspheric Lens Design

The design equation for an aspheric lens surface is given by

$\begin{matrix}{z = {\frac{\kappa\mspace{11mu}\rho^{2}}{\sqrt{1 - {\left( {k + 1} \right)\kappa^{2}\mspace{11mu}\rho^{2}}} + 1} + {\sum\limits_{j = 1}^{m}{\alpha_{j}\mspace{11mu}\rho^{j}}}}} & (1)\end{matrix}$where z is the height of the lens surface above the x-y plane and hasdimensions of length. κ is the curvature and has dimensions of inverselength and ρ is the axial distance from the lens axis measured in thex-y plane and also has dimensions of length. The expansion coefficientsα_(j) have dimensions of inverse length to the power j−1. The parameterk is dimensionless and lies between −1 and +1. For k<0, the lens has ahigh aspect ratio (k=−1 produces a parabolic surface). A spherical lensresults for k=0, and a low-aspect ratio lens with steep edges for k>0.

The parameters κ, k, and the coefficients α are selected by aminimization or evolutionary programming process to minimize the focalregion of the lens at the desired distance. Referring to FIG. 22, thefirst step is to consider the focal point at f₁ and the lens surface onthe right with parallel rays incident from the right. The designequation is used to concentrate the parallel bundle of rays tracedthroughout the right lens surface using Snell's law of refraction. Asfew expansion coefficients as are required to accomplish this task arechosen. Once a lens surface that correctly focuses the left-travelingparallel rays has been found, a left lens surface is then placed asshown in the figure and a new bundle of rays is traced from the focalpoint on the left, through the first lens surface (left surface) intothe material of refractive index n and thence through the second lenssurface (right surface). For this step, a new set of surface parametersfor the left surface are chosen. The parameters of the right surface arethen varied. This process is repeated until the bundle of raysoriginating on the left of the figure at focal length f₁ are properlyfocused at conjugate focal length f₂ on the right of the figure. In thecase of a Fresnel lens, the surface height z is stepped as shown in FIG.23B before rays are traced through the system. This process generallyconverges fairly quickly to a satisfactory set of parameters that thencan be used in the manufacturing process.

Asymmetric, Aspheric Lens Design

The above design process produces an axially symmetric lens that isoptimized for both light source and focal point situated on the axis ofthe lens. In the optical interconnect disclosed here, most light sourcesare far from the lens axis. This is especially true for large systemswith many emitters and receiver arrays. To accommodate off-axis sources,a given lens can be made slightly asymmetric so that it is biasedtowards focusing light whose source is a point lying away from the lensaxis. Equation 1 expands the lens surface in a simple polynomial in ρ.Replacing the sum over powers of ρ with a sum spherical harmonics allowsa general representation of a surface that is not necessarily axiallysymmetric. Such a surface will have lumps or bulges to correct foroff-axis light sources.

The design process to asymmetrize a lens is to first design an axiallysymmetric lens as in the previous section. To this approximate lenssurface add a spherical harmonic of the formα₂(A ²−ρ²)×ρ⁻¹ or α₂(A ²−ρ²)(x ² −y ²)ρ⁻²   (2)where α₂ has units of inverse length, A is the aperture radius,ρ=(x²+y²)^(−1/2), and x and y are Cartesian coordinates in the planewith z the axis of the lens. The coefficient α₂ is adjusted as describedabove to place the lens focus of an off-axis source at the desiredposition and minimize the focal region, which will now exhibit coma andspherical aberration. This process may be repeated with the nextspherical harmonics of the next higher order until the desiredtolerances on the focal position and size of the focal region areachieved. Any reference on orthogonal expansions, such as OrthogonalFunctions by G. Sansone, Dover Publications, New York will provide thenecessary functional forms for use in this procedure.Light Budget for a Square Array of Nodes

The light from each emitter should be spread so that every receiver isilluminated. In practical terms, this implies that the lens above eachreceiver array should be sufficiently illuminated by each emitter in thesystem. Unless optics, such as prisms and optical wedges, are used, thelight from any emitter should effectively span the largest dimensionacross the array of nodes. If the array is square or rectangular inshape, this dimension is the diagonal. If the array is circular, thisdimension is the diameter of the circle. This maximum dimension of theplanar array is reduced slightly by the twice distance of an outsideemitter to the edge of the array. Thus, if the emitters are as shown inFIGS. 20A-20B or FIGS. 21A-21C, and the node face is a 50×50 mm square,the reduction is approximately 25(2)^(−1/2) mm. If there are 25 suchnodes arranged in a square, the radius of the light cone, when reflectedto fall back onto the array of lens structures, is (2)^(−1/2) (5×50−25)mm or approximately 320 mm. Without optics to fold back light that wouldotherwise fall outside the node array upon reflection or miss the mirrorentirely, the light will be uniformly spread over an area of about320,000 mm², assuming a uniform illumination within the emitter beam.Since the maximum area of the collecting lens, in this example, is 50×50mm² with a 10 to 20% reduction for the area required by the divergingoptics, the fraction of light falling on any lens structure and hencefocused onto any receiver is the ratio of these two areas, or about0.8%. This is further reduced by reflective losses and irregularities inthe various optics.

In a square array with the light-collecting per node area proportionalto the dimensions of the face of the node, the fraction of lightcollected is given by

$\begin{matrix}{\frac{2}{\left( {{2n} - 1} \right)^{2}\mspace{11mu}\pi}\mspace{11mu}\varepsilon} & (3)\end{matrix}$where n² is now the number of nodes in the array and ε is the efficiencyof the optics and accounts for reflective losses, loss in area due tothe diverging optics (the small lens inserts shown in FIGS. 23A-23B),and any empirical imperfections in the optics. Typically, ε is about 0.4for the multiplicity-4 structure (see FIG. 21B) and 0.3 for amultiplicity-1 lens (see FIG. 21A).

The typical, commercially available photoreceiver has a sensitivity ofabout −21 dBm (about 8 μW of optical power). The active region is in theneighborhood of 0.2 mm on a side for an area of 0.04 mm². Ideal opticswould focus the image of each emitter precisely onto a spot of 0.2 mm indiameter centered on the photoreceiver. If the spacing betweenphotoreceivers is a small fraction larger than their width, any smallimperfections in focus or alignment, or any mechanical vibration, wouldcause unwanted cross-talk between receivers. From a mechanical alignmentand robustness perspective, it is a good idea to place thephotoreceivers as far apart as possible within the constraints imposedby the physical size of the node face. Robustness against misalignmentand mechanical instabilities is then achieved by focusing the light inan area centered on each receiver. Of course, an additional micro lensmay be placed just above each receiver to concentrate the spread-outbeam onto the receiver.

Suppose the configuration constraint is to choose anemitter-to-corner-receiver distance to be the same as thereceiver-to-receiver distance, then a node such as depicted in FIG. 21B(i.e., four emitters or a multiplicity of k=4), would have a spacing ofs/2(2n+1) between receivers where s is the dimension of the side of thenode face. This is shown in the node depicted in FIG. 21B with n=6. Theoptimum diameter of the focused spot is now s/2(2n+1) instead of themore restrictive 0.2 mm. The ratio of the areas of the optimum-diameterspot to the ideal spot is the excess power factor needed to adjust theemitter powers so the receivers have adequate power with thismechanically optimum receiver spacing. For small arrays, the spot sizecalculated by this method is usually larger than the 1 mm or so that issufficient to satisfy all but extreme cases of misalignment orvibration. For larger arrays, this, spacing can be in the few hundredmicron range, indicating that custom-designed and fabricated receiverarrays are required.

Mechanical Stability & Focal Spot

If the collecting and focusing optic is placed at the optimal positionwith respect to the receiver array, each emitter image formed by theoptic will lie in precise registration with the corresponding activearea of each receiver. Since the receivers are typically a few tens ofmicrons in diameter, and a larger area implies a slower response, theoptimum focus position is also the most unstable to lens imperfections,mechanical misalignments, and mechanical vibrations. Such imperfectionswill lead to momentary loss of communications while misalignment tomechanical shock may lead to permanent loss of communications. By movingthe collecting and focusing optic closer the receiver array, the focalpoint on the node face becomes a focal region surrounding the receiver'sactive area. The optimal diameter of this focal region is the spacingbetween receiver centers. Of course, the light intensity at a receiveris lower within the focal region than at a focal point with the smallerdiameter of the receiver's active area. To compensate for this loss ofintensity at the receivers, more powerful emitters can be used.

The distance from the node face layer to the plane of the lens structurecan be adjusted to establish the proper focal region. The configurationof regions is shown in FIG. 24.

Referring to FIG. 24, the concept of under focus is depicted. Thecollecting and focusing optic 2410 is represented by the large oval onthe left. The dot on the far right is located at the focal point of theoptic 2420. The cone of light 2430 is represented by the triangularshaded area and the receiver in the plane of the node face 2440 by thesmall white oval. The dotted oval surrounding the receiver lies in theplane of the node face and shows the extent of the focal regionassociated with the each receiver 2450.

By choosing a lenslet array to include converging lenslets (positivefocal length), the array of lens structures can be placed closer to thenode face. On the other hand, an array of diverging lenses (negativefocal length) allows the array of lens structures to be placed fartherfrom the node face. Such fine-tuning might arise when the divergence ofthe emitters needs to be matched to a certain sized diverging optic inthe lens structure.

Electro-Optical Layer

To achieve an efficient coupling of n nodes, each emitting and receivingmodulated light in a broadcast mode, where each node can receive opticalsignals from every other node simultaneously, an optical system isrequired. First, the optics should sufficiently spread out light fromeach emitter so that each receiver is illuminated. Second, this mixtureof light from all emitters that falls onto each receiving node should bespatially de-multiplexed into separate beams so that each node receivesa distance light beam from each emitting node. This can be accomplishedby the optical interconnect layer disclosed herein.

The next stage in establishing an interconnection of an array ofprocessing modes should consider the conversion of electrical signals tobe sent from processing elements to optical signals for transmissionwithin the device. This stage also needs to consider the reception ofoptical signals by a suitable optical structure, and a conversion of theoptical signals back to electrical signals for use by the processingelements.

The receivers and emitters, along with associated drivers and amplifierscomprise the electro-optic portion of the node. These parts can bemounted on a printed-circuit board (PCB) or a multi-chip module (MCM)substrate; this submodule can be termed the electro-optic (EO) layer.The context of the free-space, optical fan-out broadcast interconnectdisclosed herein can include an electro-optical interconnect thatperforms an electrical-to-optical (EO) conversion as well as anoptical-to-electrical (OE) conversion. The optical interconnect is thestructure that interfaces the EO portion to the OE portion so that theresulting system has the desired property of establishing fast andefficient communication channels between processing nodes (modules). AnEO layer including emitters, receivers, and associated electronics isdepicted in FIGS. 25A-25B.

Referring to FIGS. 25A-25B, a node face 2550 is depicted in FIG. 25B andthe node back 2500 is depicted in FIG. 25A. The node face 2550 isdepicted without the lens structure, which would be mounted onstand-offs above the face 2550 shown in FIG. 25B. These illustrationsshow a conceptual rendition of an MCM node with the EO layer in FIG. 25Band the processor nodes 2510 (modules) in FIG. 25A. The shaded squaresin FIG. 25B represent the circuitry necessary for transductingelectrical signals for conversion to and from light signals. Thiscircuitry can include serdes (serializer-deserializer) elements 2560.Other modules 2570 contain the necessary transimpedance amplifiers,decoding circuitry, and any required local storage. The four opencircles represent the four emitters, one serving each processor node.The black dots represent the photo-receivers, one for each emitter inthe system. A fully functional interconnect for a multiprocessing systemwill also include logic and local memory for routing and temporarystorage of messages.

Simple and Compound Lightnodes

Typically, a lightnode has one emitter for each processor node, althoughthis is not a required constraint as processing nodes (modules) may wellshare light emitters by temporal multiplexing. A lightnode also containsan array of receivers that belong to a single processing node (module)or are shared among a group of processing nodes (modules) associatedwith the particular lightnode. If the emitters and receivers lie in thesame plane, the emitted light passes through the array of lensstructures before it reaches the mirror which folds the light back ontothe collecting optics.

As previously noted, a preferred embodiment of a node in the inventionincludes four emitters. In this case, a receiver array services fourprocessing nodes (modules) by local (within the node) electrical fan-outfrom each receiver to all four processing nodes (modules) and electricalfan-in to each receiver from all processing nodes (modules). Local logicwithin this electrical multiplexing of signals from receivers toprocessing nodes (modules) controls the multiplexing switches byallowing information destined for a particular node to reach that node.

As also previously noted, advantages of an interconnect constructed frommultiplicity-four nodes (four emitters to one node) include a factor of4 less receiver arrays and associated circuitry within the system, 4times the light intensity at any given receiver for an emitter of agiven power, and four times fewer nodes and associated lens structures.Other advantages include a larger node face with more space for thereceivers. This also implies that the daughter cards for the processingelectronics (discussed in the section on processing nodes) can belarger. Disadvantages are that the lenses are larger implying that thenumerical apertures of the individual collecting lenses should be largerfor a given mirror distance.

Each lightnode should contain local multiplexing circuitry in additionto the header-decoding circuitry. The lens structures are more complexin containing four diverging elements instead of one. By increasing thenumber of processing nodes (modules) per lightnode beyond 4, theelectrical multiplexing issues become more severe and the wire lengthsbecome longer. At some point, diminishing returns of advantages overdisadvantages will arise. Certain configurations of processing nodes(modules) are better met with multiplicity 4 or multiplicity 8lightnodes in spite of the rising disadvantages.

Emitters

Emitters may be lasers, groups of lasers of different wavelengths,light-emitting diodes, plasma light sources, or any other structure thatis capable of supplying modulated light, whether visible, infrared, orultraviolet. Each emitter or light source within a compound emitter(cluster or group) requires driving (modulating) circuitry to modulatethe device itself or an external structure capable of modulating lightemitted by the device.

Receivers

Receivers may be photodiodes of suitable sensitivity. A receiver may besensitized to a particular wavelength by design as in U.S. Pat. No.5,965,873 by Simpson et al. or by a wavelength filter placed over thereceiver either separately from or integral with a light-collectingmicrolens. Receivers based on photomultipliers and photo-sensitivechannel plates are also possible approaches to light detection for theinvention.

Receiver Array

The electronics (transimpedance amplifiers, limiting amplifiers, anddeserializers) associated with a lightnode's receiver array may beintegrally contained with the receivers or separately bonded to acircuit board containing the receivers and emitters. An integratedreceiver array or a discrete array of receivers may be covered by amicrolens array to gather more of the incoming light onto each receiverelement.

Methods of Light Modulation and Demodulation

U.S. Ser. No. 60/290,919, filed May 14, 2001 and PCT/US02/15191, filedMay 13, 2002 (published Nov. 21, 2002 as WO 02/093752) all by Brian T.Donovan et al. all disclose generating electrical pulses of widthsprecisely controlled to sub-cycle precision. Donovan et al, U.S. Pat.No. 6,445,326 discloses approaches to providing sub-cycle precision inmeasuring pulse widths. Dress and Donovan,U.S. Ser. No. 10/175,621,filed Jun. 20, 2002 and PCT/US03/19175, filed Jun. 18, 2003 bothentitled “Pulse Width and/or Position Modulation and/or Demodulation”disclose modulating and demodulating electrical or optical pulses withsub-cycle precision. By applying aspects of these modulation anddemodulation technologies directly to the laser driver for modulationand at the receiver array for demodulation, it is possible to achieve aspectral efficiency significantly greater than 1. Thus, the bandwidth ofthe optical interconnect disclosed herein can be increased by 4 or 8 ormore times over that of simple pulse-amplitude modulation of light aspresently practiced. The choice of which modulation and demodulationtechniques to utilize in an embodiment can be made based on achievinghigher data rate and achieving higher noise immunity.

The laser drivers may be directly modulated or modulating signals may beapplied to acousto-optical devices positioned after the light source,whether lasers, light-emitting diode, plasma, or other such source oflight. Pulse-width demodulating circuitry may be integrated with thereceiver array, allowing an inexpensive and compact receiver arraycomplete with electronics to be achieved.

Additional light modulation may achieved by using modulatedradio-frequency signals to drive an acousto-optic element as in U.S.Pat. No. 5,146,358 by William M. Books. Such modulation and attendantdemodulation can achieve higher signal-to-noise ratios and increasedsensitivity over the simple modulation and demodulation discussed above.

Lens Placement

Since light impinges as different angles depending on the source andlocation of the lightnode within the lightcube, lens structures allcentered over their receiver arrays will image the array of emitters atdifferent locations with respect to the center of the node face.However, ease of manufacturability suggests that a single design for thenode face be replicated and identical parts be used to construct theinterconnect system. There are several ways to overcome the problemimposed by the manufacturability constraint being inconsistent with thefact that different lightnodes receive light at different angles. Sincethe effect of different reception angles appears as an opticaldistortion of the image plane that contains multiple images of the arrayof emitters, an optical correction is possible by replacing the planarmirror with a spherical mirror centered over the center of the array ofnodes. The method preferred in the present embodiment, however, is toposition each image of the array of emitters so that the image is inperfect registration with the receiver array and each receiver array iscentered in the face of its node for ease of manufacturability. Thisrequires a translation of the collection optic of the lightnode's lensstructure in a direction towards the center of the array of nodes and atan amount proportional to the distance of a given lightnode's receiverarray from the center of the EO array. An example of this translation isillustrated by FIG. 26 and can be term asymmetric optic alignment.

Referring to FIG. 26, the placement of lens structures for a 3×3 nodearray is depicted. The lens structure belonging to the center lightnodeis placed precisely at the center of the receiver array as shown by thebold, circled cross 2610 in the center of the FIG. 26 since the lensstructure is illuminated symmetrically from all directions in that thereis an equal amount of light coming from the left of the vertical dottedline and impinging on the center lens structure as there is light comingfrom the right. Two of the other three axes of symmetry are also shownas dotted lines through the center of the figure. The position of thelens structure in the upper-right corner is shown by the bold, circledcross 2620. Note that this center is no longer at the center of thereceiver array 2625, represented by the array of 36 small circles in theupper-right lightnode square. Two other lens-structure centers areshown, one to the right of the center and the other above the center.The marked positions 2630, 2640 are closer to their respective receiverarrays than the center in the upper right, but are still biased towardsthe center of the figure. This asymmetric optic alignment when appliedto all of the non-central optics results in the image of the array ofemitters being in substantially perfect registration with all of thereceiver arrays. In an alternative embodiment of the invention, one ormore of the receivers can be spatially biased (asymmetricallypositioned) with regard to the node array and/or the optics array toimprove registration of optical signals with the plurality of receiversthat define the receiver array.

Processing Layer

The optical interconnect or backplane or fabric disclosed hereinprovides a simple and effective solution to fully interconnecting largenumbers of intercommunicating functional elements or circuit modules.The set of elements can be homogeneous or heterogeneous in theiroperation on the received messages or data. Examples of homogeneousprocessing elements would be a supercomputer including a large number ofidentical computing nodes or a communications switch likewise includinga large number of identical identification, correction, and routingnodes. A heterogeneous system might have a mixture of general-purposecomputing nodes, as well as specific purpose nodes for carrying out suchfunctions as encryption and decryption, message-traffic analysis, imageprocessing, mathematical functions such a matrix inversion or polynomialexpansion, high-level symbolic processing, as well as many otherpossibilities. A reconfigurable, heterogeneous processing system wouldallow the replacement and regrouping, either physically or logically, ofa mixture of such specific- and general-purpose processing nodes. Theonly requirement is that communications nodes in the electro-optic layerare properly interfaced to processing nodes (modules) in what can betermed the processing layer. The communications layer (opticalinterconnect layer and electro-optical layer) would be consistent infunction across the system and that each processing node (module) have aconsistent interface to the communications layer. In a homogeneous viewof communications, the processing layer is simply an array of processingnodes (modules) that communicate with the EO layer through the opticalinterconnect layer.

Processing Node and Lightnode

The electro-optical portion of a lightnode may be thought of asincluding of a single compound lens structure that spreads out a lightbeam (from a laser, light-emitting diode, etc.) from one or moreemitters and is able to focus light reflected off a mirror or screenonto one or more focal points. Each focal point has a receiver orphoto-sensitive detector for detecting or receiving a light signal froman emitter residing on the same lightnode or elsewhere in the opticalsystem. Thus, a lightnode can defined by a single compound lensstructure that forms an image of all emitters in the system onto asmaller array of receivers plus the associated electronics including theassociated emitters and receivers. In addition to forming an image ofeach emitter in the system, the lens structure contains structure thatspreads out the associated emitter's light (fan-out) so that each partof the system receives a portion of the emitted light (broadcast).

If there are n² emitters in the system under consideration (note changeof notation for convenience only) and each emitter has its own lenselement, then that lens element can focus all n² emitter images onto anarray of n² receivers located in the focal plane of the lens element.The lens structure can be larger than the EO layer only for thoselightnodes not in the interior of the lightnode array. Light at theedges of the node array that escapes collection by the variouslightnodes can be used for off-array communication. FIG. 27 illustratesthe portion of the processing layer associated with a lightnode's EOlayer. Note that this configuration is not uniquely determined by thelightnode geometry. A smaller number of wider processing daughter boardscould span a collection of nodes and be attached thereto by a system ofconnectors or cables.

Referring to FIG. 27, a lightnode 2700 is depicted without the lensstructure, which would be mounted on stand-offs to the right of FIG. 27.A PCB version is depicted including four processing modules 2710 each ofwhich includes four package chips 2720 (e.g., processors, memory, etc.)represented by shaded rectangles. The EO layer is at the right of thefigure with the array of black dots representing the receivers 2730 andthe four open ovals representing the emitters 2740 (e.g., lasers or LEDsor plasma emitters).

Another configuration of the processing layer segmented to match eachnode is shown in FIGS. 28-28B where daughter boards are replaced by thedense packing allowed by MCM techniques. In this embodiment, theprocessing layer associated with the node is located on the back side ofthe EO layer whereas in FIG. 27, the processing layer included fourprocessing modules mounted on daughter PCB cards attached to the back ofthe node's EO layer.

Referring to FIGS. 28A and 28B, a node 2800 is depicted without the lensstructure, which would be mounted on stand-offs above the face shown onthe right. This illustration shows a conceptual rendition of an MCM nodewith the EO layer on a front side 2810 in FIG. 28B and the processornodes on a back side 2820 in FIG. 27. This version illustrates fourprocessor modules 2830 in this single node. The shaded rectangles(representing unpackaged die) in FIG. 28A depict the four processors,each of which may contain multiple processing elements. Memory 2840 isrepresented by the small shaded squares. The shaded squares in FIG. 28Brepresent the circuitry 2850 necessary for transducting electricalsignals for conversion to and from light signals, namely the serdes(serializer-deserializer) elements, as well as the necessarytransimpedance amplifiers, decoding circuitry, and local storage. Thefour open circles represent the four emitters 2860, one serving eachprocessor node. The black dots represent the photo-receivers 2870, onefor each emitter in the system.

The Full Optical Interconnect

A multiprocessing system can be defined to include a number ofindividual processors linked by either electrical or opticalinterconnections, or a combination of the two. Additional linkagesconnect processors to local and/or remote memory. One or more processorscan reside on a single chip or die. Groups of processor chips, alongwith power, random-access and other forms of memory storage, memorycontrol circuitry and other elements form a processor node (module) asdescribed above.

A processor node including packaged chips will typically reside on aseparate PCB that is attached to the EO layer either directly, through aconnector, or through a cable. If the processors are based on bare die,which are much smaller and can be assembled in higher densities thanpackaged chips, processor nodes can be placed on the back side of the EOlayer greatly reducing the volume of the node. The node concept can bethought of as containing multiple general-purpose computing nodesserving as a component of a high-performance computer or supercomputeras well as multiple specific-purpose switching or routing nodes. Inaddition, there are other specific-purpose devices such as messageexamination nodes, encryption and decrypting nodes, processing nodes formathematical functions, etcetera. A combination of these functions,depending on application requirements, is achievable by populatingvarious nodes with different functional processing nodes (modules) arerequired by any particular application.

The Electro-Optical, Optical-Interconnect Cube

A collection of nodes (with their associated lens structures) can bearranged in a square array and support attached or remote processingnodes (modules), form the computing cluster or computing array. A mirroror screen placed above the plane of the lens structure couples the lightemitted from each node to other nodes in the system. The entire assemblyincluding the mirror or screen layer, the array of lens structures, theEO layer and the processing nodes (modules) can be termed a lightcubebecause the shape of the complete system is roughly that of a cube withthe dimensions of the mirror being similar to the dimensions of thearray of EO submodules, and the distance of the mirror from the EO layerbeing close to a side of the array of EO submodules.

An individual lens structure may be mounted on each node or an array oflens structures may be similarly mounted above or beyond a planar arrayof nodes. The electro-optical and optical interconnect portions of alightcube are shown in FIG. 29.

Referring to FIG. 29, a lightcube 2900 is depicted based on a 3 by 3array of nodes 2910 where each lightnode contains four processor nodes(modules). The lightcube can include three layers. On the left is the EOlayer 2920 of 9 nodes 2910. Only the emitters and receivers are shown.In the PCB version, circuit boards (not shown in FIG. 29), attached tothe back of the EO layer, would extend farther to the left. In the MCMversion, processing nodes would be mounted directly on the back of theEO layer with signal-conditioning circuitry mounted on the front asillustrated in FIGS. 28 A and 28B. The next layer, slightly to the rightof the EO layer, represents an array of 9 lens structures 2930. Eachlens structure can include four diverging elements to achieve fan-outconsistent with the overall image forming geometry. These opticalelements are shown as the four small ovals in each lens structure, for atotal of 36, matching the number of emitters in the EO layer. Each lensstructure also contains a large light-collecting and focusing opticrepresented by the 9 large shaded ovals. A mirror 2940, shown on theright, comprises the third layer. In this configuration, all threelayers lie in parallel planes, with the distance between the planesconstrained by the distance from the far left layer to the mirror on theright, the spacing of receivers in the receiver array, and the type offocusing optic used.

The lightcube may have processing nodes (modules) attached to the leftof the EO layer, in which case the system is a multiprocessing systemfully interconnected by a FSOI. If connectors to remote communicationsor remote processing elements replace the processing nodes (modules),the lightcube then serves as an electro-optical switch and/or routerhaving full broadcast capability.

Mirror Alignment

Geometrically, by considering the central ray from an emitter in onecorner of the array to a receiver in the other corner, the angulartolerance on the mirror is approximately the receiver spacing divided bythe array diagonal. In practice, the collecting optics considerablyreduce the severity of this constraint. The tolerance on mirroralignment is reduced by the same factor as the optics reducing the imageof the emitter array to the much smaller receiver array size. Thisincrease in tolerance is also given by the ratio of the two conjugatefocal lengths, or, more accurately, the ratio of the size of thereceiver pattern to the emitter pattern. For a node tile of side s, thereceiver pattern fits into a square of about s/2 on a side. The emittersfit into a square that is (2 n−1) s/2 on a side. Since the lensstructure images the larger square onto the smaller square, the angulartolerance is increased by 2 n−1 over an unlensed, central ray.

Feedback Control on Mirror Angle

In a typical system represented by FIG. 29, with a receiver array ofabout 30 mm and an emitter spacing of 50 mm, this ratio is ⅕, relaxingthe tolerance on the mirror angle from about 1/20 th of a degree toabout ¼ degree. The absolute mirror tolerance is roughly constant as thearray size increases since the reduction in size of the emitter image tothe receiver array should be increased. In certain situations, activecontrol of mirror alignment might be required. This can be achieved byadjusting the mirror angle via electromechanical positioners derivingtheir control signal from one or more dedicated lasers reflected fromthe mirror itself back onto CCD arrays in the receiver plane might berequired. It is known how to derive an error signal from such anarrangement of a narrow light beam impinging on a photosensitive arrayof small pixels.

Consider a narrow-beam laser mounted at one corner of the EO array and aCCD array in the opposite corner. The error signal is an x-y vector ofpixel deviations from the nominal center of the CCD array. Amicroprocessor containing a table or simple algorithm converts the x-yposition error into three differential drive signals, one sent to eachof three electro-mechanical positioners located on three of the fourcorner mounts supporting the mirror. As the signals are applied to thepositioners, the error signal is reduced. When the correct mirroralignment is achieved, the error signal vanishes, leaving the mirror inits desired position. Should mechanical dimensions change due totemperature or vibration, the error signal will reappear and the mirrorwill be re-aligned.

Receiver Lens Array

By mounting lenses directly over the receivers, for example a smalllenslet array that matches the receiver array, optical alignment becomesless critical. In this case, the main focusing optic would be designedby taking the optical action of this additional lens into consideration.The resulting optical system would be able to focus more of the lightonto a smaller spot aligned with the active area of each receiver.

Optical amplifiers can be placed above each receiver to pre-amplify thelight collected by the lens structure. Thus, the invention can functioneven though the emitted light is too weak to directly excite a receiverelement.

Alternate Embodiments

The array of nodes may be configured in arrangements other than asquare. For example, a linear array of nodes, while not making optimaluse of the light, might be a more suitable configuration for someapplications. For example, an array of 50 by 50 mm nodes in a 2 by 4configuration would measure 100 mm by 200 mm by perhaps 300 mm. Thiswould be a convenient size for portability as a flat package.

The invention can include optics designed to optimize light usage withina given configuration of lightnodes. For example, the light output of anemitter can be confined to a square or rectangular region by usingspecific purpose optics. Such specific purpose optical devices includeprisms, conical lenses, diffractive elements, binary-optical elements,and holographic elements.

The invention can be configured with unfolded optics where the emittersare removed from the EO layer and placed beyond the mirror position(i.e., with at least a portion of the mirror omitted). Two EO layers canthen communicate across a lightcube assembly without a mirror. Even inthe entire mirror is removed the individual EO layers can continue tocommunicate internally electrically, at a local level.

The invention can include the use of mirrors that redirect light intodifferent regions, angles, and directions for communication withreceivers not in the emitter plane. That is, a configuration of nodescan be arranged in other forms than lying in a plane.

The invention can include the use of corner reflectors or corner mirrorsto replace the planar mirror. This concept can be extended to morecomplicated geometric shapes having more than four corners.

The invention can include the use of dichroic mirrors allow multiple useof the light cube space. For instance, 6 EO layers can be connected tothe same cubic volume, where each layer has an associated dichroicmirror that reflects its own associated color. Light from each lightcubewould then occupy the same volume while the different colors would allowthe various lightcubes to operate independently. Three lightcubes canalso use the same lightvolume without dichroic filters.

The invention can include simultaneous, non-blocking broadcast ofinformation. Most interconnect schemes, whether optical or electrical,allow messages and information to be broadcast. However, because of theintrinsic nature of the broadcast techniques and structures disclosedherein, the invention can include broadcast that is simultaneous to allnodes in the system in that the same physical message is distributedsimultaneously throughout the system. It is also important to note thatthe version of broadcast disclosed herein is non-blocking in that amessage being broadcast to all nodes in a system does not block anyother messages from being sent from a different node at the same time asthe given node is broadcasting.

The invention can include wavelength-division multiplexing (WDM) atemitter sites & filters at receiver clumps (clusters). Multiple lasersat different wavelengths (heterogeneous, monolithic laser arrays) can beused at the emitter location in place of single lasers. Since the lensstructure reduces the image of the emitter array onto the receiverarray, each receiver becomes an array of receivers such that themultiple wavelengths from an emitter array are focused onto the receiverarray. The spacing between receivers in this local group can be largerthan the optically reduced spacing of the laser array of thecorresponding emitter. For example, a laser array with spacing of 240 μmin a system with emitters (arrays of lasers) spaced by 40 mm would havethe corresponding receiver with a spacing of perhaps 1 mm between groupsof receivers (a 40-to-1 reduction in image size). If this spacing ratiowere to be maintained between receivers in the local group correspondingto the lasers in an emitter group, a spacing of 240 μm divided by 40, orapproximately 6 μm, would be needed. This small spacing may beimpractical from an optics and electronic circuitry standpoint. Thesolution is to space the receivers corresponding to a given emitterarray of lasers at a physically and electrically reasonable distance(e.g., from approximately 2 microns to approximately 2 mm) and thenfocus the light from the corresponding emitter to illuminate this largerbundle of receivers. Each receiver could then have a dichroic filtermatching the wavelength of the particular laser in the emitter's arrayof lasers. This would ensure that an array of different wavelengthlasers operating within a small region can communicate with an array ofreceivers in a one-to-one manner. Alternative embodiments of theinvention can direct the various wavelengths from the emitting array oflasers onto the appropriate receivers through the use of diffractiveelements (gratings) or dispersive elements (prisms).

The invention can include the use of diffractive lenses and binaryoptics. All techniques of forming images with light or collectingdispersed light or dispersing light may be used with the invention. Forinstance, the invention can include the use of refractive opticalelements (the commonly used lenses), lenses with graded indices ofrefraction (so-called grin lenses), diffractive optical elements such asbinary optics and holograms, light funnels, conical prisms, as well ascollecting mirrors.

Emitter Types: Plasma, Lasers, Light-Emitting Diodes

All light sources may be used for the emitter as long as they arecapable of being modulated either directly or indirectly. Directmodulation is defined, in the case of a laser, to be that the lasercavity or other intrinsic property is modulated electrically byappropriate circuitry. Indirect modulation is defined to be that anexternal modulation device such as an electro-optical absorber oracoustic-optic modulator is coupled to (e.g., placed above) thelight-emitting element so that light leaving the emitter can bemodulated before it is fanned out to reach the receiving elements.

The invention can include the use of specific purpose elements in thefold-back optics. Specifically, the invention can use prisms ordiverging lens or diffractive optics to shape and expand the emitteroutput so that, after reflection, it illuminates the collecting-lensarray uniformly as possible and with little or no light spilling overthe edges of the collecting-lens array.

The invention can include extending the folded optics in broadcast intoa spill over mode. Specifically, the invention can include adjusting thefold-back optics so that sufficient light from one or more lightnodes isreflected past the collecting-lens array. Any light uncollected andunfocused by the emitting lightcube can then be used to communicate,edge-to-edge, with another lightcube or other device such as i/o devicesor other processing elements.

The invention can include wavefront compensation. When communicating athigh data rates, a wave front correction should be made so that lightarriving at the edge or corner of a lens reaches the intended receiverwithin the same time interval as light passing through the center of thelens. As these geometrical distances are different, arrival times of awave front will be different. A signal of sufficiently short durationwould have its shape spread out in a time longer that the duration ofthe signal. Thus, one signal pulse could be confused for another signalpulse. Such a situation could arise for a system with large lenses orshort signal pulses.

The invention can achieve wave front temporal compensation by includingplacement of a conical refractive element above or below each converginglens in the lens structure. Light travels more slowly in a material withan index of refraction greater than 1 than it does in air (having anindex of refraction only slightly above 1). Typical transparentmaterials (glass, plastics) have indices of refraction between 1.3 and1.9. All of these materials can be configured in a conical shape wherethe material is thicker at the center than at the edges, forcing lighttraveling through the center of the lens to pass through more opticalmaterial than light at the edges, thus compensating for the longergeometrical distance covered by light passing through the edges of thelens. Such a conical element affects the focal properties of the lensstructure and should be taken into account during the design phase ofthe lens structure.

Since the temporal dispersion of the light wavefront grows as the sizeof the lens aperture, another way compensate for such temporaldispersion is to restrict the aperture of the collecting optic. Acompensating increase in emitter power should accompany the loss inlight intensity at a receiver.

The invention can also achieve the same effect by using a flat plate ofoptically graded material where the central portion has a higher indexof refraction that the outer portions. The grading of the index ofrefraction can be continuous to precisely compensate for the timedifferential in wave front arrival. The lens structures themselves maybe made from graded material and the design process would have twocontrol parameters to consider. In addition to the focal properties ofthe lens, the wave front properties should be taken into account duringthe design process.

The invention can include the broadcast of information contained in awavefront or the broadcast of a wavefront itself. A wavefront is anymeasurable physical change in the property of a wave. A wave is aphysical phenomenon that is describable by a wave equation. Examples areacoustic waves (both in bulk and surface) and electromagnetic waves(radio-frequency waves and light). Measurable physical changes may occurin the amplitude, intensity, polarization, phase, and frequency of awave. Any of these properties may be used to carry information byappropriate modulation techniques.

Advantages of the Invention

The invention provides advantages in the context of supercomputing.Communications between processing nodes is one of the central bottlenecks found in supercomputers. The methods disclosed herein overcome thelatency problems associated with interprocessor communications byinterconnecting all nodes in a system with light. The resultinginterconnect is smaller and faster than existing cross-bar and fat-treemethods. In addition, the invention allows efficient broadcast models tobe directly implemented rather than simulated as is presently done.

The invention provides advantages in the context of switching androuting. Configured as an optical switch, any node in the system canbroadcast information to all other nodes. If each information packet hasan associated routing header, any one or several receiving nodes thatrecognize that header can accept the information packet and transmit itout of the optical switch to the appropriate recipient.

The invention provides advantages in the context of associative memory.In simplest terms, memory association is a method of posing a query asto the presence or absence of a certain item. A code for the item inquestion is broadcast to all portions of the system. These portions aresearched in parallel and any positive responses are reported back to thequerying node. The effect is that of an associative memory. Such anassociative memory can be very large and distributed by making use ofhashing tables at each processing node (module), such hashing tablescontain references to remote memory stores such as disk drives orinternet resources.

The invention provides advantages in the context of sorting and merging.The broadcast capability allows a multiprocessor system to carry outsorting algorithms more efficiently than presently used interconnectmethods. A table or list to be sorted is broken into n small pieces andeach piece is sent to one of n processing nodes (modules) where it issorted using a standard sorting algorithm. Each processing node (module)signals when it is finished to coordinate the merging phase. Eachprocessing node (module) then sends its table element-by-element inordered fashion to the merging node where the results are placed in thefinal table in sorted order. Comparisons are done in the merging node(module) to achieve the overall order based on range informationreceived from each of the partial-sorting nodes (modules).

The invention provides advantages in the context of communicationsprocessing where one light path is used to simply transmit acommunication stream while the other n²−2 paths split up the data streaminto multiple processes on independent processors, each of which mightsearch for a different pattern or condition without affecting orinterfering with the primary communications path. The invention providesadvantages in communications processing where forward error correctioncan be effectively and efficiently done on the communications stream inplace and on-the-fly. The invention provides advantages incommunications processing where individual data packets representingvoice messages can be decoded into sampled audio, such sampled audio isthen subjected to further processing such as speaker or speechrecognition even as the uninterrupted path through the system continuesto carry the original message.

The invention provides advantages in the context of image processingwhere each portion of the image is sent to a different processor for aparticular type of filtering operation, all such filtering operationstaking place in parallel. The final image is then reassembled at asingle node in the system.

The invention provides advantages in the context of pattern recognitionon signals or images where the probabilities of certain pattern typesare desired. Each of n processors can examine a signal or image inparallel where each examination is essentially testing an hypothesisconcerning a particular pattern. The result of each individual processis a probability of a particular pattern being present. Combining theresults in the Bayesian manner yields the most probable pattern alongwith its absolute probability within the population of patterns beingsearched.

The invention provides advantages in the context of database searchingwhere each processor has access to a different database or a differentpart of a particular database. A machine with n nodes opticallyconnected as in the broadcast method allows such a search to proceed inparallel, effectively speeding up a database search by the number ofprocessors available.

The invention provides advantages in the context of pattern recognition,where data from a subset of sensors, such as a random grouping of pixelinformation from an imaging device, is sent by broadcast to specificpartial-image processors. The entire set of image-processing nodes(modules) can then identify particular pieces of the pattern inparallel. Individual pattern elements are then recognized as belongingto certain patterns. The results are assembled in a coordinating elementand the most probable pattern is identified with the presented image.The paper by W. W. Bledsoe and I. Browning, “Pattern Recognition andReading by Machine” in the 1959 proceedings of the Eastern JointComputer Conference presents a particular example of pattern recognitionthat would benefit by the broadcast method disclosed herein.

More generally, in the usual interconnection methods, typically eitheroptical or electrical (crossbar, electrical multiplexing with fan-out,etc), broadcast is achieved by increased complexity or simply notattempted other than by relaying messages between processors or seriallybetween levels of the interconnect hardware; Optical fan-out is bothinexpensive and simple to accomplish. Electrical fan-out, on the otherhand, is slow, expensive, and difficult to accomplish, introducinglatencies and delays in the message paths. The optical broadcast methoduses optical fan-out, allowing light energy to reach all parts of thesystem from each optical emitter. An added feature of using light forbroadcast is that light from various emitters does not interfere in thefree-space region where the fan-out is taking place. That is, multiplelight channels can occupy the same physical space.

The broadcast model of optical communication within a backplane allowsefficient multiple-instruction, multiple-data (MIME) operation as wellas the usual single-instruction, multiple-data (SIMD) operation.Broadcast allows parallel database searching. This can be achieved bybroadcasting a query to a distributed database where each portion of thedatabase is interfaced to a processing node (module) of the system.

The broadcast model of optical communication within a backplane allowsasynchronous operations and data-flow architectures. Synchronization canbe efficiently achieved and maintained by broadcasting short messagesconcerning global system status and reporting local processor or clusterstatus. Data-flow computations can be easily coordinated by such shortbroadcast messages.

The broadcast model of optical communication within a backplane allowsboth large-grained and fined-grained problems to run simultaneously. Inthis case, destination codes can be assigned to groups of nodes and suchnodes are not constrained to be near neighbors. Dynamic “local” groupsare may be formed where “local” has a purely logical connotation and notconstrained by physical nearness.

The broadcast model of optical communication within a backplane allowshigh-throughput transaction processing. For instance, by allowing eachprocessing node (module) in a large lightcube array to communicate withseveral transaction stations, a lightcube can handle a large number ofdistributed and local transactions. Coordination between thetransactions and a central data repository can be accomplished bybroadcasting necessary information to coordinating processors as thetransactions occur.

The broadcast model of optical communication within a backplane allowsefficient semaphore use and management. Semaphores can be used tocontrol computing resources by preempting them for in certain situationsand allowing access in others. Semaphore management can become efficientand practical in a broadcast model.

The broadcast model of optical communication within a backplane allowsmultiple hypothesis testing on a single system (e.g., Bayesian parallelprocessing). Bayesian hypothesis concatenation and the particularapplication of Bayesian signal processing are the most consistenttechniques for dealing with data of all kinds. Although preferred bymany, these computationally intensive activities are often approximatedby faster but less accurate methods. A parallel-processing system thatallows broadcast of data to multiple hypothesis-testing nodes will allowthe more accurate Bayesian methods to find wider application.

The broadcast model of optical communication within a backplane enablesdistributed memory access. A significant advantage of a low-latency,message-broadcast model is improved memory access in a distributedmemory system. For example, in a cache-coherent, uniform memory model,the addition of a new node would not be a problem as the new node wouldsimply announce its presence and any reference to the new node would besimply a reference at large, broadcast to all.

The invention is scalable and cost effective. The invention isinherently tolerant to misalignment with no feed-back recovery systemnecessary. The invention facilitates efficient optical communicationand/or computing within and between core switches, terabit routers andcross-connect equipment, especially in central office environments.

Practical Applications of the Invention

There are many practical uses for the communications power provided bythe invention that have substantial value within the technological arts.A central result achieved by the invention is that of intrinsicinformation broadcast to the entire set of processing nodes (modules).As a computing or data-processing technique, broadcast allows multiplereceiving nodes, simultaneously and without necessity of intervening anddelaying relaying steps, to receive coordinating information as well asallowing data to be processed in parallel. Practical uses of broadcastinclude synchronizing computing activities, efficient communication ofsystem control information, efficient management of semaphores (e.g.,for simultaneous updating of local cache memory from a global memorystore), implementation of a flat-memory model where a system-widedistributed memory is uniformly available to all processing nodes(modules) within a system, asynchronous routing of packet information tomultiple receivers, distributing video information to multiplereceivers, database transaction processing where a single query ispassed to multiple databases and/or distributed to portions of a largedatabase, and pattern matching wherein a pattern is broadcast tomultiple processors each of which examine in parallel a small portion ofthe image and the matching information is broadcast from eachpartial-pattern processor to a central information processor. Inaddition to processing of information, broadcast can be used toefficiently and effectively control information being sent to a varietyof receiving stations, whether local within the system or remote fromthe interconnect and accessed by Ethernet, internet, or other networksand communication channels.

There are many practical uses for the magnitude of computing powerprovided by the invention that have substantial value within thetechnological arts. The invention is useful for simulation and modelingof physical processes. The invention is useful for switching and routingof information. The invention is useful for the management of massivedatabases. The invention is useful for pattern matching andcorrelations. The invention is useful for data analysis and reduction.The invention is useful for image processing and rendering.

A partial list of practical applications for the invention include:nuclear stockpile verification; massive database searches &correlations; drug design; biological simulation and modeling; weathersimulation and modeling; physics & astronomy simulation and modeling;chemistry by design; mechanical engineering structural modeling anddesign (e.g., buildings, vehicle crash testing, etc.); earth sciencessimulation and modeling; biometrics on a massive scale (e.g., voice,face, vital signs, bio patterns, etc.) voice identification and speechtranscription on an accurate and massive scale; economic andsociopolitical simulation and modeling; automatic database creation,management, consolidation and mining; and onboard space-craft andsatellite data processing. Some applications for the invention inswitching, routing, and rendering are: automatic communications anddata-routing center, for instance, gathering, sorting, classifying,correlating, and disseminating all communications; informationmanagement and switching (e.g., a continental-scale data router or other(potentially inexpensive and redundant) continental-sized distributedsystems); pinpoint video for a mass audience (e.g., education,entertainment, and so forth); repository, storage, and deliverysystem(s); real-time film production (e.g., animation, rendering,digital imaging, etc); and a multi-player, video game server. There arevirtually innumerable uses for the invention, all of which need not bedetailed here.

The terms a or an, as used herein, are defined as one or more than one.The term plurality, as used herein, is defined as two or more than two.The term another, as used herein; is defined as at least a second ormore. The terms comprising (comprises), including (includes) and/orhaving (has), as used herein, are defined as open language (i.e.,requiring what is thereafter recited, but open for the inclusion ofunspecified procedure(s), structure(s) and/or ingredient(s) even inmajor amounts. The phrases consisting of and/or composed of close therecited method, apparatus or composition to the inclusion of procedures,structure(s) and/or ingredient(s) other than those recited except forancillaries, adjuncts and/or impurities ordinarily associated therewith.The recital of “essentially” along with “consisting of” or “composed of”renders the recited method, apparatus and/or composition open only forthe inclusion of unspecified procedure(s), structure(s) and/oringredient(s) which do not materially affect the basic novelcharacteristics of the composition. The term coupled, as used herein, isdefined as connected, although not necessarily directly, and notnecessarily mechanically. The term approximately, as used herein, isdefined as at least close to a given value (e.g., preferably within 10%of, more preferably within 1% of, and most preferably within 0.1% of).The term substantially, as used herein, is defined as largely but notnecessarily wholly that which is specified. The term generally, as usedherein, is defined as at least approaching a given state. The termdeploying, as used herein, is defined as designing, building, shipping,installing and/or operating. The term means, as used herein, is definedas hardware, firmware and/or software for achieving a result. The termprogram or phrase computer program, as used herein, is defined as asequence of instructions designed for execution on a computer system. Aprogram, or computer program, may include a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer or computer system.

All the disclosed embodiments of the invention disclosed herein can bemade and used without undue experimentation in light of the disclosure.The invention is not limited by theoretical statements recited herein.Although the best mode of carrying out the invention contemplated by theinventor(s) is disclosed, practice of the invention is not limitedthereto. Accordingly, it will be appreciated by those skilled in the artthat the invention may be practiced otherwise than as specificallydescribed herein.

It will be manifest that various substitutions, modifications, additionsand/or rearrangements of the features of the invention may be madewithout deviating from the spirit and/or scope of the underlyinginventive concept. It is deemed that the spirit and/or scope of theunderlying inventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

All the disclosed elements and features of each disclosed embodiment canbe combined with, or substituted for, the disclosed elements andfeatures of every other disclosed embodiment except where such elementsor features are mutually exclusive. Variation may be made in the stepsor in the sequence of steps composing methods described herein.

Although the optical interconnect described herein can be a separatemodule, it will be manifest that the optical interconnect may beintegrated into the system with which it is associated. For instance,the optical backplane may be part of a computer or network. Theindividual components need not be formed in the disclosed shapes, orcombined in the disclosed configurations, but could be provided invirtually any shapes, and/or combined in virtually all configurations.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” and/or “stepfor.” Subgeneric embodiments of the invention are delineated by theappended independent claims and their equivalents. Specific embodimentsof the invention are differentiated by the appended dependent claims andtheir equivalents.

1. An apparatus, comprising a free-space optical fan-out and broadcastinterconnect including: a plurality of nodes positioned to define a nodearray, each of the plurality of nodes having an optical signal emitterand a plurality of optical signal receivers, the plurality of opticalsignal receivers positioned to define an individual receiver array thatwith regard to image forming geometry substantially corresponds to thenode array, wherein the optical signal emitter of all of the pluralityof nodes and the plurality of optical signal receivers of all of theplurality of nodes are substantially coplanar; a plurality of opticsoptically coupled to the array of nodes, the plurality of opticspositioned to define an optics array whose members with regard to imageforming geometry substantially correspond to the nodes of the nodearray, each of the plurality of optics including a diverging element anda light collecting and focusing element, wherein the diverging elementsof the optics array with regard to image forming geometry substantiallycorrespond to the optical receivers of each node of the node array,wherein the diverging element of all of the plurality of optics and thelight collecting and focusing element of all of the plurality of opticsare substantially coplanar, wherein an optical signal from the opticalsignal emitter is fanned-out by the diverging element of one of theoptics and broadcast to one of the plurality of receivers of all of theplurality of nodes by the light collecting and focusing element of allof the plurality of optics; and a reflective structure optically coupledto the array of optics, wherein the optical signal is reflected by thereflective structure after the optical signal is fanned-out.